After the holes are drilled you take sand paper and rough the outside of the brass tubes, put super glue on them and insert them into the holes your drilled. This is my least favorite part. If I don't wear gloves I glue my fingers together and believe me, that glue is hard to get off your hands.
Let the glue dry and then using a special drill bit on your electric corded drill (cordless drill doesn't have enough power) you make the wood flush with the brass tubes, making sure you don't drill to much. Speaking from experience, I have thrown out a few I drilled to much.