Hey Brandon, the device you need is called a, "Digital Multimeter," or DMM for short. They can be purchased at Home Depot, Radio Shack, Harbor Freight, and most any auto parts store, or online. In my experience, the best deals are at harbor freight if you have one in your town, or online at Marlin Jones, the website is below. They come in lots of flavors, cheap to really expensive, depending on how accurate you want it to be, and how many features you need. Nice ones are tolerant to within 1/2 %, and measure temperature too, in case you want to test your refrigerator. My little $12 USD unit works just fine for testing my solar panels, even if the readout is off 5% or so,you'll still get a good enough reading on a panel, they are only guarenteed to within 10 or 15% anyway.
It sounds like you're new at this, so I'll explain how to test a solar panel. They have two basic ratings, Open Circuit Voltage, or VOC, and Short Circuit Current, or Amps. Take one panel, open the junction box on the back, set your DMM to 0 - 200 volts DC and make sure the test wires are plugged into the correct jacks. Red should be on V-Ohm-Ma, and the black to common -. Then connect the two wires to the two terminal points at the far left and right end of the terminal strip inside the J box. This should give you VOC if the panel is in the sun, and for a normal 12 volt nominal panel, I would expect to see at least 17 volts, but not more than 21. It should be very close to the VOC spec on the panels data plate on the back. If you can't get any volt reading from the two end screws, orthe readout is much smaller than you expect, try a different pair of screws, sometimes different panel manufacturers have different protocols on using the terminal strips, and it is possible to get a half voltage reading depending on how the panel is wired up if you have one of the wires on the wrong screw.
Next, reset the red lead wire to the 10 amp input, and turn the rotary switch to 0 - 10 amps DC. Now put the leads on the same two screws as before. For this test the panel has to be in good sun, not overcast weather, near mid day, and aimed directly at the sun. You should get amps very close to the data spec on the back of the panel again. When you are done, make sure to either unplug the leads, or put the red one back into the jack marked V - Ohm - Ma. If you leave it in the 10 amp jack, and then later rotate the switch to voltage to check something else, you can fry the meter if it's connected to anything that can put out more than 10 amps, like a battery or household outlet. The other item I should mention is that the panel should not have an amp rating higher than 8 amps, or the 10 amp meter might be fried by the panel. Most panels are smaller than this, an 8 amp panel will likely be taller than you are, just check first. If it is a big panel and has a rating higher than 8 amps, you will need a larger meter, or a device called a shunt, you'll have to read about it online, they do sell them for certain meters at the Marlin Jones website. Good luck Brandon, and take care, Rudydoo