As noted previously, The Bluebook is a vast, complex citation manual, and it will take some time (and a lot of patience) to learn the rules and understand legal citation. The best way to learn The Bluebook is simply to start using it.
One resource for additional practice with legal citation is Lexis's Interactive Citation Workstation (ICW). ICW is an online tutorial that helps law students build their basic citation skills. It is a good supplement to the instruction provided in introductory legal research and writing courses. Login to Lexis and go to Interactive Citation Workstation (found under the Lexis product switcher). For more information, see the LexisNexis Interactive Citation Workstation Guide for Students.