Here are a couple of videos that explain the limit of a function:
http://www.youtube.com/watch?v=-j1AV4kdgfc&feature=youtu.be
http://www.calculus-help.com/tutorials
11.1 Find limits graphically and numerically part 1: https://www.youtube.com/watch?v=gah7EInlIog
11.1 Find limits graphically and numerically part 2: https://www.youtube.com/watch?v=1jxl20_ET8M
11.2 Find limits algebraically part 1: https://www.youtube.com/watch?v=Yw8gi-fUHcs
11.2 Find limits algebraically part 2: https://www.youtube.com/watch?v=Cpqeck2g0jU
11.2 Find limits algebraically part 3: https://www.youtube.com/watch?v=aBSdi3zlFBM
11.3 Find limits at infinity part 1: https://www.youtube.com/watch?v=Raw0MkvSqqY
11.3 Find limits at infinity part 2: https://www.youtube.com/watch?v=doif-z7AhiE