Remove any charcoal basket from the bottom of your smoker. If you have a one-chamber smoker, then the charcoal basket will be on the bottom underneath the smoking racks. If you have an off-set two-chamber smoker, the charcoal basket will be on the bottom of the firebox chamber, which is usually attached to the side of the smoking chamber where the smoking racks are located.
Drill a hole through the bottom of the smoker or firebox chamber, depending on which type of smoker you have. The hole should be large enough to comfortably fit the extension pipe that fixes to your propane tank. The pipe should fit without the sides of the hole kinking or otherwise impairing it.
Place a propane burner element on the bottom of the smoker or firebox chamber and connect the extension pipe to the burner.
Thread the pipe through the hole in the bottom of the smoker and connect the other end to the propane tank. You can now use the smoker with propane instead of charcoal.