In one sentence, describe what the following article is about:

" This very common, albeit somewhat informal greeting, is pronounced roughly like "cheh-sh-ch." Non-Poles may find it difficult to pronounce this word correctly. Following a "sh" sound with a "ch" sound is something that is almost never done in English.  "Cześć" is a little informal to use in serious social situations. While it's fine for friends and family members, some etiquette-conscious Poles may be offended if you use it the very first time you meet them.  "Cześć" may also be used to say "bye." " This is pronounced as "DOH-bry VYEH-choorh." "Dobry" is pronounced the same way as in "dzień dobry." The W at the beginning of "wieczór" is pronounced like a V, not an English W. As in English, this greeting is used when meeting people after the sun has begun to go down but before it has gotten completely dark. "Dobry wieczór" has the same level of formality as "dzień dobry." " This is pronounced exactly like the English "hey." It is a very familiar and informal greeting. You won't want to use it for formal situations or people that you're interested in maintaining a professional relationship with. It is best used among close friends. "Hey" in Polish works the same as saying "hey" in English. This word is pronounced as “vee-tahm.” The W in the first syllable is pronounced like the English V. The second syllable has a soft "ah" sound, as in "apartment." "Witam" is not always an appropriate greeting, especially to strangers. It can subtly imply that you occupy a higher social station than the person you're talking to. It is best reserved for when you are greeting guests to your home.

Summary:
To say "hello" in Polish, say "cześć. To say "good evening," say "dobry wieczór. To say "hey," say "hej. Say "witam" when you are greeting guests and you are the host.