How do you know if you like someone or if someone likes you?

If you like him then when you're near him you might feel tingly, say stupid things or speak in a different voice then you usually do. If he likes you then he should be doing the things listed above.

No one can answer that question but you.
Each person is different.
If you don't know if you like him and we are on the internet how am I supposed to know never seeing or being around either of you?

Have you ever liked someone?

I could answer like some others and say, "Girl! Do you find yourself thinking about him at random/odd times? Do you ever have him pop into your dreams? Do feel or act different around him... like not yourself, uncomfortable or all butterflies in your stomach?" but yeah it takes a little time to know. Give yourself a chance to find out. Symptoms vary. Some people are more cool and collected but maybe inwardly they just question, like you are... give yourself more time around this person MORE and THEN you'll really begin to tell & answer your own question. :)

Liking someone is more than just a feeling and feelings are deceptive