I have an amaryllis growing in a pot in the house. I want to save the
seeds when the flower is spent. How do you pollinate the plant?

Transfer pollen from the stamens to the stigma of a flower... generally best
to do this several days running, because stamens and stigmas generally don't
mature at the same time. You'll see the young fruit start to swell a few
days after the flower fades if your pollination is successful.

A couple of things to think about: you're unlikely to make great breakthroughs
in plant genetics with this sort of casual plant breeding. And the process
of making seeds takes a lot of energy from the plant, so your parent plant
may not bloom well again for a year or two. But it's a fun thing to do,
and the seedlings are simple enough to raise.

Kay