SO I have picked up playing the guitar. It has six strings and is a fretted musical instrument.
Are there any variants other than the six string version?
I think Keith Richards plays a 5 string guitar. I have been playing an electric guitar. The sounds is projected through an electrical amplifier.
Do you know when the guitar first gained popularity
There were many different types that preceded the guitar. There was the vihuela, gittern, four-course Renaissance guitar, and baroque guitar.
Are there any types of music that the guitar is particularly popular in?
The guitar is hugely popular with modern rock music. The guitar is played by using your fingers to pluck the strings. 
Are there any other instruments that compliment it well?
guitar, and the archtop guitar, which is sometimes called a "jazz guitar". The tone of an acoustic guitar is produced by the strings' vibration, amplified by the hollow body of the guitar, which acts as a resonating chamber. The classical guitar is often played as a solo instrument using a comprehensive finger-picking technique where each string is plucked individually by the player's fingers, as opposed to being strummed. The term "finger-picking" can also refer to a specific tradition of folk, blues
Guitar
The guitar is a fretted musical instrument that usually has six strings. It is typically played with both hands by strumming or plucking the strings with either a guitar pick or the finger(s)/fingernails of one hand, while simultaneously fretting (pressing the strings against the frets) with the fingers of the other hand. The sound of the vibrating strings is projected either acoustically, by means of the hollow chamber of the guitar (for an acoustic guitar), or through an electrical amplifier and a speaker.
The guitar is a