To hold the blank you can clamp it against the drill press fence, use a carpenter's clamp to hold it, or use a jig like the one pictured. It is very easy to ruin a blank by drilling too fast. A parabolic flute bit is excellent for expelling the chips. Now you're ready to glue the brass tubes into the blanks. Read the instructions that came with the pen kit to determine which tubes to use with which blanks.
Test fit the tubes to ensure that they slide in easily.
Rough the outside of the blanks up with a fine grit sandpaper to remove tarnish and ensure proper bonding. Now you need glue. Put a few drops of your glue in the end of the blank. Let it run to the other end while turning it to spread it out on the inside. Slide the tubes into the blank and set them on wax paper to dry.