Champions.
Assasins/ Mages: They are usually used in the mid lane.(Said who plays Ahri supp.) but it's your choice the lane you choose with them. (Katarina, Lux, Zed, Veigar etc.)

Marksmans: They are usually used in the bot lane, as ADC but some of them can be used on mid lane or in top lane, in mid lane champs like Varus (Like Power of evil) or Ezreal with AP runes, masteries and items. This champ can be used with AP things because it's ''hybrid'' it can be used AP or AD. In the top lane champs like Quinn or Vayne are not bad at all, I remember that in one game there was a Vayne jungle, and it was nice too. Anyway this champs are mostly used in the bot lane. (Ashe, Jinx, Lucian, Caitlyn..)

Fighters: They are used in top lane and jungle, but they are used in mid lane too because there are champs with two roles like zed (Assasin and Fighter) (Riven, Darius, Garen, Irelia, Poppy..)

Tanks: These are mostly used on top lane, in jungle or bot lane as supports. (Supports like: Thresh, Leona, Alistar..) (Top laners like: Malphite, Cho' Gath, Nasus..) (And junglers like Rammus, Skarner, Shyvanna..)

And finally Supports, they are in the bot lane with an ADC and there are two types: Tanky supports (Leona, Braum, Blitzcrank..) or AP supports (Lux, Morgana, Lulu, Karma, Sona..)

After all of this the only thing I need to say it's that any champ can go where it's player wants, it's true that some of them are more viable that others in some lanes, but the most important thing is that you're having fun with the champ you choosed and that you know how to use it.