You could fancy your chances in at hooker - weight isn't everything unless you're playing proper seriously. Provided your set-piece work is good and you're good in the loose (Tackling, hitting rucks, carrying etc) you'd fit in fine imo.
If you're new to the game, however, most coaches will just stick you on the wing for the time being.
In terms of on the pitch stuff, make your tackles (Go low, keep your head on the right side and drive your legs), don't drop the ball, listen to your teammates and (Most importantly imo) don't be afraid of going into contact. The first hit is always tough to get your head around, but after that it'll become second nature.
Hope this helps