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)