How do you pump and BF at the same time?

I feel so stupid asking this I did it just fine with ds1. But I didn't pump with ds2 or ds3. Now ds3 is 11m and I'd like to have some milk available. My mom wants us to go to a movie tonight but I have no milk so it'll have to be timed perfectly. Ds3 eats alot, and usually takes both sides. Everytime I've tried to pump I only get a few drops at a time. If I wait until he's been asleep for an hour or so, I won't have enough milk when he wakes up. If I give him food instead then doesn't that start the same cycle as forumula supplementation? Sorry for asking something so basic, I forgot how to do this part

ETA Clarification: by same time I don't mean simultaneously, I mean how do you pump extra for storage while still feeding enough to the baby. Hope that makes better sense.