Depends on the buns :lol: Some just get on with it, others need assistance. I drilled a small hole in mine and have it attached to a piece of wire which runs along the flap on the outside and up the shed wall - I actually leave it open all the time; they know how to use it but it's right next to the neighbour's house and the catflap was annoying them when it kept bashing all night :lol:
I'd suggest propping it open for a few days (maybe jam something stable that can't be knocked over or pushed out the way under it) so they get the idea of coming and going, then close it and see what happens!