How do I sand drywall?

A sander with an attachment bag to suck in the dust that you can dispose of when the bag is full.

You can’t. The best you can do is tape and drape everything, do not use a fan in the room or open a window to cause a draft, and remove anything you can from the area to keep plaster dust off it.

Remember to vacuum as you go, replace you vac bag after the job.

Don't sand! We finish drywall by using a damp sponge. Keep 2 large buckets. The first you immerse your sponge and wring out. Rub in a circular motion. When it's "full" of mud, dip in 2nd bucket until fairly clean.

I've been doing this for over 10 years with great results and virtually dust free. I used to use a car wash sponge but you can find a variety of sanding sponges in the big box stores. Some of them are even specialty sponges. Here are a couple of examples.

https://www.homedepot.com/p/MAT-Drywall-Sanding-Sponge-105900B/100020608

https://www.homedepot.com/p/3M-Pro-Grade-Fine-Angled-Drywall-Sanding-Sponge-30904FPSA/202074119

Save yourself a lot of headaches go with the sponge and bucket routine. You will probably still have some sanding, But greatly reduced

Wet sanding is best

Drywall finishing makes tons of dust! Unavoidable if you want excellent finishes. DO drape and block HVAC outlets. Do use a fan in open windows facing outward.

Once finished, carefully and slowly sweep from the ceiling down to remove all dust on the ceiling and walls. Slowly sweep the floor and dump the dust in a plastic lined garbage can. Once you've removed all dust that can be swept up, use a shop vac for the remainder. It isn't helpful to try to vac up all the dust initially as you'll immediately clog the shop vac.

When you've finished sweeping and vacuuming, use only COLD water to sponge up the remaining drywall dust. Rinse your sponge often so you aren't spreading more dust around. It takes at least 3 cold water rinses to remove the remains.