i want to get a h22a

if i get a h22a what should i expect, do i need motor mounts, and when i want to add aftermarket part for ex. if i want a header back exhaust system should i get one for a 94 accord or for a prelude?

You should expect to get what you purchased. Where are you looking for your H22a? You wont need motor mounts unless the H22a you do buy doesn't have them. What do you mean by "when i want to add aftermarket part for ex." For the header question, I believe you need H22a Headers with a Accord exhaust.

ex stands for example. how will the prelude header fit one the accord cat?

Well all you have to do is make sure the diameters are the same. I would assume if you are getting a header-back exhaust you would either swap in a testpipe or a high-flow cat in place of hte Accord cat. So find out what diameter the h22 header will be, and build from there. It isn't too hard to mix and match, and if all else fails, you can have a custom catback built on to whatever hi-flow cat or test-pipe you decide on. Really it shouldn't be much of an issue if you just focus on everything staying the same size. That is more important than if everything mounts up to the stock exhaust hangers, but I doubt even that would be a problem, it just might require a bit more searching.