What do you do if you like a girl but don't know how to say it?

Try asking him and one of his friends to do something in a group setting if you're nervous about asking him out. It's not directly saying, "hey, let's go on a date." But it is (should he be able to pick up on it) giving him a sign that you're interested. If he doesn't say anything afterwards, try asking him out alone. You never know what he'll say until you ask.