The tags on champions are relatively reliable, but they're not concrete.
Also, many of us highly recommend finding one or two champions who feel 'natural' to you and you're ok with (as in, you like their abilities and you don't think you suck horribly with them) and practice the game with them. There's a lot of knowledge in LoL about team composition, if champ A is shut down hard by champ B, and so on. It's tricky to learn and can't be done all at once, but if you know how one or two champions work and how they relate to the others, you'll have a solid foundation for the game and its mechanics.
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~Peaf~
"Later that day, I f***ed a panda." - PSO