Help me with the basics please.

[limit refugee]

Agree with Nick above, just adding that idjits love to make small bets with the flush draw to price themselves in, and it is your job to not let them. His turn bet screams it, so you have to raise, plus its the easiest way to make sure stacks go in. His big bet on the river telegraphs his hand, so at that point, you can't raise it.