This is based entirely on reading old books, I've never cut a gear
this way. I buy them.

The teeth of a hob are cut to the shape of a rack, meaning that the
tooth flanks are straight at the pressure angle. Machinery's Handbook
shows the dimensions.

First you rough out most of the tooth spaces in the gear blank with a
normal milling cutter on a rotary table. Then you put the hob on the
spindle and set the blank up beside it on an arbor that can turn
freely without play. The arbor has to be angled so it's parallel to
the hob's spiral teeth. Slowly feed the gear blank into the hob, which
will rotate the gear and automatically generate the proper involute
tooth form as the hob teeth roll in and out of mesh. Whether or not
the tooth spacing stays accurate depends on friction and how much
metal the hob has to remove. If possible the spindle should drive the
arbor through gears.

Although you have to harden and grind the hob and may have to try a
few times to get a good gear, hobbing lets you make gears of any tooth
count with correct involute teeth starting from a lathe bit ground to
a simple straight-sided shape.