I'll probably miss a couple, but the main reasons for betting are:

For value - probably have best hand, bet to win $'s with it.
For protection - a decent hand on a drawy board and you want to charge any draws.
A bluff - you just want your opponent to fold.

People generally bluff too often, but one key is to have a believably strong hand that will get them to fold hands better than yours but not as good as the hand you're pretending to have.

Onto your hands:

Hand 1 - Probably a fold PF, but as it is you raise the flop. This is mainly value, but somewhat for protection v's a draw. When he calls some alarms should go off. What worse hands is he calling your raise with here? When the 2nd J hits the turn, the amount of possible hands you beat just decreased dramatically. Why are you betting now? Its unlikely to be for value anymore, and draws only make up a small portion of his range. At this moment you should be hoping to showdown as cheaply as possible, but instead you're bloating the pot. Ask yourself why you bet the turn?

Hand 2: Flop bet is good. Again its mainly for value, but also protects yourself from overcards hitting on the turn. When he calls and the worst one does, you need to evaluate your options. Remember the A is a scare card for him as well as you (if he doesnt have one), but you put in a really small weak bet, which allows him to call with weak hands he might otherwise fold. You're not telling a convincing story here. Your bet doesnt make sense if you're ahead of him (which is what you want him to think).

Hand 3 is fine, nice c-bet.

Hand 4 is fine, you want to take him to value town here.


So get what I mean about thinking about WHY you're betting, and betting in a way to achieve that aim.