What does it mean and when can I use it?
This is for comparison. I cannot sing as well as her. I do not speak Spanish as well as he does.
As well:
It usually goes at the end of a sentence and is used like the words TOO and ALSO.
After you order water at the restaurant, I might say to the waiter: I'll have water as well.
You're learning to speak English? I'm learning a second language as well!
Erica and Jian have got this one covered for you but I would add that "well" can be used as an indicator of quality (as in "well done", "you have done well") and therefore you just need to be aware that "as well" or "as well as" can also be used as a comparison of that quality / skill level.
Compare the examples below:
"No, no, I don't play football as well as tennis. Just tennis." (as per Jian's example above)
"No, I can't play football as well as I play tennis. I'm not very good at football." (comparison of skill level)
"I like to eat a lot of meat but I do eat my vegetables as well." (could be replaced with "too")
"Harry speaks excellent French, he is often mistaken for a native. I don't speak French nearly as well. (comparison of skill)
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-We might as well. There is no other way to get to the center."
So, "might as well" means yes, it's a good idea or something like that.
