I've been trying to figure out that answer to that specific question for a long time. But all guys are different. One might make friendly conversation, the other might tease you, or the other might be really shy and not say anything to you. So it depends on the guy and how close you are right now like friends, best friends, enemies, etc..
You should be able to see his reactions to you. He will be looking at you, smiling at you, trying to get closer to you, and laughing to funny things you say. Those are some things that you can notice when a guy likes you.
They'll act differently around you. Maybe if they're talkative, they'll talk much more (or much less) and if they're pretty quiet, they may be silent (or quite loud.) They'll probably stare a lot, or flirt to try to get your attention. They may show off (physically or intelligence wise.)