Tire Inflation Issue

[pikato]

Forgive me in advance, I know I've read about this somewhere on here, but I guess I"m not typing the right words into the Search box.

Tomorrow, I'm doing a group ride & went to air up my tires for the first time. I have Presta valves &quickly figured I had to unscrew the little bolt thingie, but nothing happens except I'm letting air out. I even have a converter thingie to take the bike to a gas station air pump, but I can't even check tire pressure correctly!!!

What in the world am I doing wrong??

P.S. I'm going to continue to search the boards in hopes of finding the answer.