Is that what the kids are calling it now a days???
Before running full pelt into it, give it a gentle nudge with your head to check your silly owner hasn't locked it, you'd look really stupid running into it. If open, stick your head through, At this point you should be able to squeeze a leg through, first one then the other. When both front legs are through, you should be able to take a few steps forward until your back legs are near the door. If your inconsiderate owner has fed you a few too many tins of chow, your belly may scrape at this point, consider sleeping less or chasing more birds if this is the case. Now step one back leg through, then the other. Now run fast to avoid having your silky tail slammed in the door. THAT is how to work a cat flap. (sorry, you didn't ask much of a question, if you give us more details on what you want to know you might get a more sensible response)
+1 That's the way I do it. Actually for me, it is a larger door, the kind intended for a dog, but it works just the same.
My cat's method, if she knew I was around, was to sit outside and yowl pityfully until I pushed it open for her. If I wasn't there she would shoot through, no problem at all.
How big is this cat then? L