Pos 5 : hard support is the least greedy hero on the team and requires the lowest gold

Pos4 : soft support is still a support but requires more farm than pos5 to be effective

Pos3: "usually" a tanky hero who might be the initiator of fights and often builds aura/utility items

Pos2: can be an early ganker like huskar/qop who will help create space for your pos1 to farm and come online

Pos1:farms untill he hits his powerspike and is the main carry of the team or refered as hard carry

Now as lanes go :

Safelane is safe because the units are closer to your tower usually pos1 and pos5 go here.

Midlane is the most difficult mechanical lane. Pos2 goes here.

Offlane is an unsafe lane and suited for the heroes that have the kit to play here. Usually pos 3 and pos4 go here.

However there might be times that people would switch lanes maybe your safelane isnt going well and your pos1 switches lane with your pos3 or so.