How to Become a Muslim
Question

How to become a Muslim and how to take shahadah?
Praise be to Allah.All praise be to Allah, the Lord of the universe. May peace and blessings of Allah be upon Mohammad, His last Messenger. 
Do you need witnesses to become a Muslim?
The purpose of this answer is to correct a false idea spread among those willing to adopt Islam as their faith. Some people have a wrong notion that entering into the Islamic fold requires an announcement from the concerned person in the presence of high ranking scholars or shaykhs or reporting this act to courts of justice or other authorities. It is also thought that the act of accepting Islam, should, as a condition, have a certificate issued by the authorities, as evidence to that effect.
Is it difficult to become a Muslim?
We wish to clarify that the whole matter is very easy and that none of these conditions or obligations are required. For Allah, Almighty, is above all comprehension and knows well the secrets of all hearts. Nevertheless, those who are going to adopt Islam as their religion are advised to register themselves as Muslims with the concerned governmental agency, as this procedure may facilitate for them many matters including the possibility of performing Hajj (Pilgrimage) and ‘Umrah.
How to convert to Islam and become a Muslim?
If anyone has a real desire to be a Muslim and has full conviction and strong belief that Islam is the true religion ordained by Allah for all human-beings, then, one should pronounce the “shahadah ”, the testimony of faith, without further delay. The Noble Quran is explicit in this regard as Allah states:
“The Religion in the sight of Allah is Islam” (Quran 3:19)
In another verse of the Quran, Allah states:
“If anyone desires a religion other than Islam (submission to Allah), Never will it be accepted of him; and in the Hereafter he will be in the ranks of those who have lost (their selves in the Hellfire).” (Quran 3:85)
In addition, Islam is the only religion prevailing over all other religions. Allah states in the Quran:
“To thee We sent the Scripture in the truth, confirming the scripture that came before it, and guarding it in safety:…. (Quran 5:48)
Muhammad, the Prophet of Allah (peace and blessing of Allah be upon him), said:
“The superstructure of Islam is raised on five (pillars): testifying that there is no God (none truly worthy of worship) but Allah, and that Muhammad is the Messenger of Allah, performing the prayer, paying the Zakah (poor-due), fasting the month of Ramadan, and performing Hajj.” 
How to pronounce Shahadah
The Shahadah can be declared as follows:
 “ASH-HADU ALLA ILAHA ILLA-ALLAH WA ASH-HADU ANNA MUHAMMADAN RASUL-ALLAH”.
Shahadah in English
The English translation of the shahadah is:
“I bear witness that there is no deity (none worthy of worship) but Allah, and I bear witness that Muhammad is the Messenger of Allah.”
Conversion to Islam should be based on full conviction
However, it would not be sufficient for anyone to only utter this testimony orally either in private or in public; but rather, he should believe in it in his heart with a firm conviction and unshakeable faith. If one is truly sincere and complies with the teachings of Islam in all his life, he will find himself a new born person. 
This will move him to strive more and more to improve his character and draw nearer to perfection. The light of the living faith will fill his heart until he becomes the embodiment of that faith.
What would be next after declaring oneself a Muslim? One should then know the real concept underlying this testimony which means the oneness of Allah and meet its requirements. One must behave accordingly, applying this true faith to everything one speaks or does.
The meaning of the Shahadah
What do the words of the “Shahadah” signify? The significant point which every Muslim must know very well is the truth that there is no God (deity) to be worshipped other than Allah. He-glory be to Him – is the only true God, Who Alone deserves to be worshipped, since He is the Giver of life and Sustainer and Nourisher of mankind and all creation with His unlimited bounties. Man must worship Allah, Who Alone is worthy of worship.
The second part of the Shahadah “i.e., Wa Ash-hadu anna Muhammadan ‘abduhu wa rasuluh” means that Prophet Muhammad (peace and blessing of Allah be upon him) is the servant and chosen Messenger of Allah. 
No one must have two opinions about this matter. In fact the Muslim has to obey the commands of the Prophet (peace and blessing of Allah be upon him), to believe him in what he has said, to practise his teachings, to avoid what he has forbidden, and to worship Allah alone according to the message revealed to him, for all the teachings of the Prophet were in fact revelation and inspirations conveyed to him by Allah.
What is worship according to Islam?
What is the meaning of worship ? It simply means rendering sincere service, showing reverence for Allah. In a deeper shade of meaning, it implies total submission and complete obedience to Allah’s commandments both in utterances and actions of man whether explicit or implicit.
What are the forms of worship in Islam?
Worship falls into two categories:

Visible (manifest or outward).
Invisible (concealed or inward).

Visible worship includes acts such as uttering the two parts of the “Shahadah”, performing prayers, giving Zakah (the poor-due), recitation of the Quran, supplication, adoring Allah by praising Him, purifying our bodies before prayers, etc.
This type of worship is associated with movement of the parts of the human body. 
Invisible worship is to believe in Allah, in the Day of Judgement (in the Hereafter), in the Angels, in the Books of Allah, in the prophets of Allah, in the Divine Decree of destiny (that good and bad are determined by Allah Alone).
This type of worship does not involve movement of parts of the body but it surely has bearing on one’s heart which subsequently affects one’s way of life. 
It should be borne in mind that any worship not dedicated to Allah Alone will be rejected as one form of polytheism and this causes apostasy from the Islamic fold.
What’s after taking the Shahadah?
The next step for a new revert to Islam is to purify himself by taking a complete bath. He should then resolve to comply with the principles and rules of Islam in their entirety. He should disown all forms of polytheism and false beliefs. He should reject evil and be righteous. Such rejection of evil and being righteous is one of the requisites of the motto of Islam – that is, La ilaha illallah . 
Allah states in the Holy qur’an:
“…whoever rejects evil and believes in Allah hath grasped the most trustworthy hand-hold, that never breaks…” (Quran 2:256).
We have to consider that when we declare from our heart that “there is no god (deity) worthy to be worshipped but Allah”, it implies on our part love, devotion, faith and obedience to the rules of Islamic legislations which are legally binding on all Muslims. It is a requirement of “there is no god worthy to be  worshipped but Allah” to love for the sake of Allah and to reject for the sake of Allah.
This is the firmest anchor of belief which materializes the meaning of “AL WALA” and “AL BARA”. It means that a Muslim should love and be loyal to his Muslim brothers. He should, as a practice, dissociate himself completely from the unbelievers and refuse to be influenced by them, both in worldly and religious matters.
We conclude with a humble prayer to Allah that may He cleanse the hearts and souls of those who are genuine seekers of truth and may He bless the community of believers.
For more about Islam, please see these answers: 10446 and 13569 .
And Allah knows best.