how old are they?
depending on age they will learn themselves. you dont need to put them there, in fact young chicks prefer to sleep on the ground in a huddle,as if in a mommy's nest. let them learn themselves. they will use it when they are older. its good if they balance on it in the day though!
9 weeks is about when my chicks learned (they are now 14) they need to learn to balance during the day so they can sleep on it at night. even now some of mine loose their balance. depending on the breed and the chick they will learn at different times!
My new chicks are 7 weeks old and have been roosting for at least 2 weeks now. They do however still like to lay on the ground or floor quite a bit. When they were younger I put a stick across a corner of a box so that they could start thinking about balancing. Worked great. They will get it eventually. Make sure it isn't too high for them to jump to.