He tell you.
Well, it mostly help to get a life and stop trying to find stupid things like this over the internet..
You can tell that a boy likes you if he looks at you a lot or he will send you a note sating that he likes you
you know if a boy likes if he gets nervous when he is around you, stumbles alot when he sees you, and he is always finding an excuse to talk to you.
All I can say is, unless you know them in person (from the way you structured your sentence i would estimate you are in education, I apologise if I am wrong), don't meet them or anything of that sort with out your parent/guardian or others knowing where you are and who you are with. You can meet dangerous people on the internet.
The best way to know is to ask him.
if he farts on your face
Ask him
when he does anything to talk to you
He talks to you.
He likes you that is what is important. it doesn't matter who else knows you.
how you will know if a boy really likes you he will act all shy around you and he will blush sometimes. and when you talk to him he will not know what to say.! fingers crossed that he likes you honey!
get to know him!