Warnberg, welcome to the board, Most any question you will have will have a specialized board listed under the "Forums" at the top of each page.
PADI, SSI, YMCA and all over the alphabet soup of smaller organizations. If you liked your instructor from your basic open water. . . you can just throw him more money, and keep with the same organization, or jump to any other organization. The requirements are different for each.
There are "courses" out there to nickle and dime every diver they can find. For a real diving education. . . go diving. You can learn more in a weekend of diving than you can playing 15 minute tango with an instructor that's out for a buck.
Fresh or salt water diving, both require you to buy air. . . That's where you'll find dive partners. Be honest with a potential partner, plan an easy dive, and go get wet! You are certified to dive in open water, just do it.
A new diver blowing bubbles is going to scare the sealife into hiding. OK, just keep blowing bubbles and work out your bouyancy. . . If you entered the water from shore . . . follow the slope out till you are comfortable then follow the slope out till you are back ashore, there you've navigated.
Gain your experience by diving, you'll learn by doing, better than by buying patches and more cards. For a complete list, click on forums and look at warm water diving, Ice diving, travel, underwater photography, wreck and cave diving, mixed gas deep diving, spearfishing and all the other things divers do underwater. Some require a "patch" or card, but all require lots of experience. Show up at a resort with a buch of patches, and you'll dive with the other beginners. . . show up the same place with a log book of a couple of hundred dives, and they'll talk about the better dives.