Well, usually its one of two ways, not sure with HBO, but for example.
HBO Uplinks its suite of channels to a satellite (for all cable providers, dish, directv etc), the providers use a dish to receive the HBO suite, then each provider compresses and encrypts the HBO signal, reuplinks it (in the case of dish/directv), or sends it over fiber/coax, to your home.
OR, Cable providers have a fiberoptic link to an HBO "distrobution" facility, in which the suite of channels is sent over fiber, then uplinked to a dish/direct satellite (or broadcast over cable lines)
I do beleive that HBO goes route 1 however, but thats the jist of it for all the channels!