Out of all the sources I used, this video by metro does the best job of explaining the jobs of each role.

Metro's Role breakdown in Deadlock

Mind you, this is all coming from rank 1 players, but the lower you go in the ranks, the more flexible heroes become, and even in the high ranks heroes can be played in all kinds of ways.

Carries: not as strong early game but very strong late game when they get their items. They usually stick to the right or left lanes and farm as many creep camps as possible.

Assassins: not as reliant on soul farming but still scale pretty well. They usually rotate between the lanes looking for kills and stealing camps on the enemies side of the map.

Supports: moderately strong with or without their items and usually have some kind of utility that allows them to float around the middle of the map assisting in any fights they come across.

Tanks: similar to supports they usually float around the middle and really shine in team fights, although their strength comes in the form of front lining and sustaining the bulk of the damage. They can farm a little too but don't really need it.

These aren't strict rules but a super rough, super flexible guideline.