1st step Get a piece of metal pipe, usually 4-5 in long or 10-12 cm long.
2nd step Put an end cap on one side of the pipe and fill it with gunpowder, tannerite or another combustible compound.
3rd step Put an end cap on the other end of the pipe and drill a small hole in this end, this will be your fuse hole.
4th step Put a fuse in the previously drilled hole. Lit and enjoy.
Note Do not use this tutorial for malicious intent. pipe bombs are only legal if register with the ATF and always remember to check your local and state laws.