There are a couple of circumstances that you will play-in on short:
1. u got really good hands and if u do have good pockets, do it before preflop - that way u get rid of anyone that is chasing a flush and u know whom first off have decent hands.
2. u r in last position (so big or small blind) and its only 1-3 people in and u have decent hands (or shiet) but everyone else has only called preflop. U r stuffed if anyone else around the table has good hands.
3. u hit a
full house or high K-A flush on the flop.
You know you should really read up on: position betting and also when to call, raise and fold on pre-flop, flop, turn and river.
People go all in pre-flop when they have a really short stack but umm.. its easy to get knocked out. so dont ever play restless, kiddies.