Answer 1: Take a college course.
Answer 2: You can learn by the 'Dowling' method, which can be found here - http://www.rci.rutgers.edu/~wcd/Latin.htm
For this method, you need the Wheelock's Latin textbook and the Lingua Latina: Familia Romana first book. Wheelock's should run you about $1.00 (Don't bother with a nice one, you will only be using a few pages of it.), and the Lingua Latina can be found for under $15.00 at amazon.com, and $15.00 or more elsewhere.
What I would recommend is this: Print this page out and staple it together, put it in a nice binder or something to protect it if you can. Read carefully through it, then write down the basic concepts of grammar. (What the Nominative, Genitive, etc are.)
Then after you've done that, you don't actually need to write down the tables 600 times like he says. If you know how you usually remember things, then memorize the tables in that fashion. I made some tiny palm sized books by folding 3 by 5 index cards together, then wrote one declension/case per page, and then covered the outside with plastic. You could also use some tiny composition books. Take one of these with you wherever you go, and then do your best to memorize.
His method is the best I have found. I didn't understand anything at all until I came across it. Now Latin is starting to be comprehensible. And best of all, this method is cheap. It just takes work.