What's this website?
I've searched in this community, but I can't understand.
Is this website supports Ad Hoc only, or it supports TestFlight / App Store also?
If you have a developer account in the App Store then you can sign up for the Companion beta program (I think you can sign up a few more users as well). This exists because the beta program is full and no more users can be added. In any case there is no need to sign up for it as Companion is already available in the store for everyone
Hmm.. Ok! It's about companion, so I can't distribute my apps to App Store yet?
No, and a simple search of the forum would have answered that for you.