First off, Lizgirl, take a deep breath. Blow it out hard.
Now, do that again.
There, isn't that better.
Learning about meat is an on-going task. Just about the time you think you have a handle on it they change the names; or introduce new cuts; or something to confuse you.
With that in mind, your best friend is the butcher or meat cutter behind the counter. Tell him/her what you are planning, and ask for a suggestion. And explain any difficulties you may be having. Those people love to be asked.
Next, despite what you read, never, ever, start with frozen protein. Even fish will turn rubbery if you start with it frozen. So make sure the protein is fully defrosted. Even better is to start with it at room temperature (don't let the food police know I told you that, though).
Now then, as to pork roast, there are several cuts to consider, depending on your desired end result.
Tenderloin is a small cut, usually packed two-up in a cryovac bag. Together they way maybe 2 lbs. Tenderloin is the tenderest cut of pork, and should be cooked quickly. If you want it whole, sear it on all sides and finish in the oven at 350 for maybe ten minutes. Use your thermometer to assure it doesn't get overcooked.
Speaking of thermometers, do not believe the figures printed on the side. They refer to the final temperature. Depending on size of meat, you want to pull it when it's about ten degrees less than that. As the meat rests it will continue to cook, and will reach the desired state of doneness. For instance, if you want a beef roast medium, you don't cook it to 135-140. You cook it to 125 or so, and let it continue cooking while it rests.
Back to pork. The next best cut is the loin itself. This comes in full pieces of up to about 10-11 pounds or so, or pre-cut to pieces ranging from a lb to 5 lbs. To visualize what the loin is, imagine boneless, center-cut pork chops. Glue them together into a cylinder and you have the loin.
Loins are used whole, or cut in thick slices, depending on how you want to cook them. As a roast they are often stuffed (various ways of doing that). As slices they are made just like boneless pork chops.
A roast that will be sliced at table most often is made with the loin.
Another great roast is made from the fresh ham. For some reason they're not as available as they used to be, but they make really great meals. Google fresh ham and I'm sure you'll find lots of recipes.
For stewing, pulled pork, and similar fall-apart uses, the shoulder and neck are choosen. The shoulder comes in two parts. The whole thing, which is the shoulder and the leg down to the "elbow" is called a shoulder. Either of those pieces alone are called butts, or Boston butts.
Do not ask me why the front end of a hog is called a butt, cuz I can't help you with that.
In any case, with those cuts, low and slow is the way to go. The shoulder is most often used for barbecued or pulled pork, for instance. When I make it I cook it on the grill, with offset heat, for from 12 to 24 hours, depending on size. In the home oven, try it at 250 degrees for, oh, six or eight hours and see what happens.
Finally there are cooking methods using wet heat; stews, tagines, braises, and ragouts for instance. These usually result in juicy, tender meats. But there can be more involved than throwing the foodstuffs together with some liquid, and you'll want to learn the specialized techniques before cooking that way.