STB = set top box (aka cable box)

If you don't know what a Cablecard is, you probably don't need one. The most common reason to get one is if you own a Tivo (the card lets the Tivo unscramble channels directly without needing a separate STB). For a while there were also some TVs on the market that accepted Cablecards so you could plug the cable in directly without a separate STB, but those TVs are rare. Cablecard never really caught on for anything other than Tivos and some homebrew DVRs because it's a one-way technology. Devices with cablecards can't get the interactive program menus that cable company-issued STBs and DVRs can (Tivos have to get their program guides separately over an internet connection). And cable companies hate Cablecard because it doesn't allow them to sell you pay-per-view.

I'm pretty sure the HBO, Showtime and Cinemax packages include all the various channels. See the second link in post #52 above (which may be a bit outdated, but gives you an idea).