Hand 1. K3 is an easy fold against a raise. At low stakes like .10/.25, solid, tight-aggressive play will win pretty consistently. The opponents will make plenty of poor and mediocre plays, so you just have to wait until they do so when you have a big hand.
Hand 2. I agree with scrawnybob. Calling after the flop doesn't really help you gather information to help you make better decisions as the hand proceeds. If you're ahead, you want to raise to build the pot and to put the onus on the opponent to make what you hope will be a difficult decision that they might well get wrong. If the opponent folds, you win a decent pot. If you're called, you can assume you're up against some kind of hand - hard to say how good, but if you raised enough, you're probably not being called with just a draw. If you're re-raised again, you can fold quite easily. Don't worry that you got bluffed; eventually, the same thing will happen when you hold the nuts, and you'll win the money back plus a lot more.
When the third 5 comes on the turn, fold seems weak. You're only behind a hand holding the case 5, AA, KK and QQ. Yes, you could lose your stack here, but I think you rate to be ahead a good majority of the time.
Hand 3. There's nothing you can do when you're opponent hits something like a two-outer on the river. You want to have all your money in as a better than 90% favorite; if those odds aren't good enough for you, give up poker.