This wrench can accommodate from #0 to 1/2" taps. The following picture shows it holding a 4-40 and 3/8-16 tap.
For instructions on tapping along with other metal working basics, watch this video.
A brief summary: First, use some sort of oil or cutting fluid, we recommend Tap Magic. While pressing down firmly, make 2-3 complete revolutions. After this, rotate forward a quarter revolution, and then backwards a half revolution to break off chips. If it gets stuck, back all the way out and clear out the chips, never force the tap. You may be able to reverse less often, but be careful. A broken tap can be almost impossible to remove, and usually cannot be drilled out because taps are harder than most drill bits.
The most critical part is starting straight. The following picture illustrates the use of a tapping block–a block of metal with holes slightly larger than the tap. You can also put the tap in a drill press and turn it by hand.