Have a multimeter,now what—
Fool around with it. Try some of these:
Shuffle your feet across a carpet, touch something grounded, get a little zap.
Set the meter on Voltage (DC), do it again, hold one lead and touch the other to the grounded item, see how charged up you are. (If you see 10,000 volts, remember it’s static electricity–if it was 10,000 volts AC or DC, the current would be deadly.)
Set the meter on current, do it again, hold one lead, ground the other, and watch the momentary reading of current. Didn’t take any time for your static charge to drain off, did it?
Check a power outlet for voltage. An outlet has a charged lead, a return lead, and many have a neutral. Set the meter for AC and test between each combination of two. Is it 110 V or somewhat different? Which is the hot lead? It’s supposed to be at the smaller slot.
Note your meter leads can be handled so they don’t touch each other while testing the outlet. If they do you get a short which will blow the fuse, heat the leads, and may do other damage. Avoiding this is not just a matter of controlling your hands, you may need to take environment into account, ie your younger brother may bump you at the wrong moment, so you don’t give him the opportunity.
Use the DC to check batteries. Does a freshly dead battery have voltage? Does it supply any current worth mentioning? It may supply enough to give heat. I wouldn’t try the current test on a good battery, since basically you’d short it out and there would be too much heat.
Set it to ohms and see how much resistance there is in metal, cantaloupe, etc. See how much resistance there is in one inch of dry skin vs. one inch of sweaty skin. You have just invented the lie detector. Try tap water vs. water with salt in it (the salt dissolves into ions with charges, so current can pass using the ions).
See what you see. And if it’s the least bit interesting, get a book or a mentor and learn the fundamentals.