There is no "role" in each lane, and strategies can be very malleable. Which becomes an issue you might encounter in pubs.
There are 3 potential styles that will be played every time in pubs if you're new and at a lower mmr.
the 2-1-2. It used to be the most common, but I don't think it is anymore. Basically you have your hard carry safelane with a support to babysit him and try to zone out the enemy offlaner(s). The mid plays mid, and of the offlane consists of a second support and a (generally) semi-carry offlaner.
2-1-1 + Jungle. Same as 2-1-2, except you now have a single offlaner and a jungler. The offlaner will generally have more escapes, and not need a support to help them survive their lane. This is the most greedy lineup in pubs, not counting 5 core lineups which generally don't work with good supports on the enemy team.
3-1-1. Mostly same as the 2-1-1 + Jungle, except you don't have a farming jungler, you have 2 supports helping the carry or the offlaner. This more or less guarantees the hard carry gets every single last hit and is not pressured by the offlaner if the tri-lane is played in the safelane. If you trilane in the offlane, the point is to kill the enemy hard carry when he tries to go for last hits, effectively zoning out the enemy hard carry, leading them into a difficult late game.
There are other playstyles which you could see a lot of in pro matches or higher MMRs, and they will be imitated in lower MMRs sometimes. A roaming Mirana trying to shoot arrows into ganks is an example of a strategy that works very well if the Mirana player knows how to aim her arrows, and gets attempted in lower level pubs, wasting the mirana's time, and if she gets too close, sapping a lot of the laner's XP while she tries to set up ganks. Roaming supports constantly ganking is an amazing strat, but again, tough to pull off if the lowskill players don't expect constant roaming ganks and just want to focus on their last hitting. Tons of stuff.
//I typed out a rant here but deleted it since it was a bit rage-y and opinionated a ton. But I just want to say - There is no "right" role for every hero. For one example (of many) Axe, who is generally played in Jungle or Offlane can also be played as a mid. That goes against the status quo or whatever and will get a lot of bitching. But it's possible. Try not to become one of those players who thinks that each hero has a lane they are associated with. They can be played in many ways. There's a video from a few days ago about a Carry Io. I didn't see it myself, but heck, I can believe it.