How do you check transmission fluid on a Chevy S10 5 speed manual tranny?

There is a plug on the side of the tranny. take it out. If fluid runs out, put the plug back in the hole and get on with life.

If no fluid runs out, check your manual for what transmission fluid to use. Fill it till it runs out at the plug a bit.

Be sure to use the transmission fluid recommended for Chevy S10 5 speed manual transmissions.