The belt goes on exactly like it is drawn in the parts breakdown.
One pulley should be V groved while the other 2 are flat.
the back of the belt runs over the flat6 pulles & the front runs over the V pulley
So laying under it like you were standing in front of it looking towards it and got mowed down :laughing:
The belt runs around the engine pully then rins down the right hand side directly to rear pulley.
From there it comes back up the left side of the mower, runs around the V pulley nearest the edge 180 degrees then around the flat pulley on the middle another 180 degrees.
From there it passes on the right side of the front fixed pulley which is in the middle of the deck ( left right wise ) and back to the engine.
This front idler pully has a bad habbit of falling off which will leave the belt very slack.
You will need to apply the brake which will cause the belt to run slack to put the belt on and even then you might need to remove one of the pulleys.
Also check that the belt did not slip off the rear pulley, they have a tendency to slip off & get caught between the fan & the pulley.
You will find it much easier to remove the deck , drain the fuel then stand the mower up on its bum so everything is right there in front of you.
So a block & tackle over a tree branch or a ratchet or some thing like that is worthwile