Find the noise
I remember the feeling of having absolutely no idea how something worked or how to fix it.
A grinding type noise could be a derailleur-ft or rear-slightly out of adjustment.Generally that isn't a big deal, and it probably won't hurt to ride the bike.
Get a few inexpensive tools-
1)Metric allen wrenches-3 to 8mm-Harbor freight-cheap, maybe $5 for the set.
3) Screwdriver(with both types of tips)-I like the ones with magnetic tips you can store in the handle-phillips and regular tips-ratchet action and a big ball handle is sometimes helpful.$3
Sears craftsman tools are pretty nice-sturdy-but you might want to buy less expensive stuff 1st.Really nice tools make the work easier, but inexpensive tools are ok.I would get metric wrenches and sockets next, and a cable cutter-a good one-soon.
Start with safety stuff.
1)Check the brakes.They should stop you from 15 mph(pedaling hard but not super hard) in about 3-4 seconds maybe 20 feet.Do the levers stop before they compress to the handle bar.Are the cables in good shape-slide freely, no rust ? Cable cutters so you can install new cables are a good investment(don't cheap out too much on the cable cutters-cheap wire cutters don't work very well for cleanly cutting the casings that the wire cables run thru)
2)If the handlebar and stem firmly attached-no slipping/moving-pointing straight forward?
3)Are the wheels fully seated into the frame "notches"-dropouts.Are they held in tightly-the quick release levers should take some effort to close and open if they are properly shut?Not superman effort, but not really easy either.
4)Tires look ok-no dry sidewalls-no slick hard tread. Tires lose traction as the age-3-4 years is too old for max traction on a wet street.
Put the safety stuff first, and check what those websites have to say about brake adjustment.Fool around with them to get the hang of it.If you change something to do with the brakes, always do an immediate road test(in a safe place-in front of your house, not a busy street) before hitting the road.