First of all: Boys aren't an alien species. There isn't a special way to talk to them all, because they are all different from each other just as girls are. It's easier to get to know someone, whoever they are, if you talk to them one to one, so if you feel a bit shy or unsure, there's nothing wrong with being a bit quiet in groups. When you are one to one, let's say with a boy you like but don't know well, it's quite natural to feel embarrassed, even scared. Here's the secret: He'll feel the same. So ask yourself: What would make me feel better right now? A friendly smile, perhaps? Some casual remark, not clever or anything?
If you imagine the person sitting next to you is shy and nervous of you, it's very easy to find something to say to them. As for rumours, these are spread by stupid people with miserable lives - if you are going to care what stupid people say you will never have any life at all, because you will find such people everywhere you go. So just act as if they didn't exist.