Hi Darstan64 and welcome to our Forum!
It's exciting to see a newcomer to Sims 3. It makes us all remember when we first started playing the game and were learning so many things that were confusing at first. I've noticed that you've made a few threads to get some answers to your questions and that's perfectly fine. However, please be careful about changing the subject when you make follow up posts. When that happens, things get off topic and disorganized, and we try to keep the Forum tidy. In fact, considering your newness to the game, I would suggest you make a thread on the Miscellaneous Help board specifically just for you instead of making new threads that end up scattering things around. You could call it something like "New Player Needs Lots of Help". That way, you can just ask whatever question you need and the rest of us can read the history of what you've already asked in order to understand your questions better. I also highly recommend that you look at Carl's Sims 3 Guide if you haven't already. It's a wonderful resource for everything about Sims 3 and the Expansion Packs. Much of the information you've asked about can be found on the Guide.
Click here to visit Carl's Guide.More in reference to this thread, I think we got confused when you used the term "roommate" to describe the other Sims in your household. Roommates are a brand new thing that just came with the University Life Expansion Pack, as MissPlumbBob explained. Roommates live in your house, but are not part of your household... meaning you cannot control a roommate. However, if a Sim is in your household and has an icon on the left side of the screen, that means you control that Sim. Sims join your household when your Sim marries or invites a Sim to move in.
Also adding to what MissPlumbBob said, I do not recommend that you start using mods (game modifications). They can be tricky and are known to mess up your game if not done properly. As a new player, I really think you should just play the game as it is. We always advise caution when using mods and third party custom content (items created by someone other than Electronic Arts).
Good luck with your game and happy Simming!