The three pronged jack plugin is for a mic cable like this -



The two 1/4 inch plugins above that are for speakers.  Plugging one speaker into each side will give you a stereo output.  The dial above those plugins is your volume control for each speaker.  If the red light comes on and 'clips' that means there's too much juice and needs to turn down.  The speaker cables are slightly different and look like this -




Finally, if it comes with a cable that is a blend between these two that can also work for a mic.  That looks like this -

This is both a speaker, and a very basic 2-channel mixer.

The two inputs are not for speakers, they're for you to plug in a mic, an instrument, or any audio (from a computer, phone, etc.), hence “input”. They can accept XLRs or 1/4" jacks. The knobs are for adjusting the volume of that input (although “volume” is not technically the correct word). In general, for mics you would need it to be higher (turn the knob clockwise), and for instruments and audio you wouldn't, otherwise it would cause clipping and distort the sound.

That single XLR (three-prolonged) output is for “looping” or “routing” audio. If you have another speaker, it can receive audio from this speaker. Or it can go into a recording system, etc. The sounds from the 2 inputs are combined before being sent out via the output.

You can adjust the high and low (bass) frequencies using the two equalizer knobs. The knobs should be at 12 o'clock by default. If the sound feels too bass-y and boomy, reduce the low frequencies, if the sound is too sharp and piercing, reduce the high. Or increase the other.

I wouldn't know too much about the wireless mic function, it varies from product to product.

To test the speaker, just plug-in a working mic, instrument, or audio into the first input, turn the knob up (clockwise) and listen for sound from the speaker. If there's sound, it works. Turn the knob all the way down, and try with the second input. Always make sure your volume knob is all the way down before plugging in or out.

This is a good speaker, and can be quite convenient, because it doesn't need a mixer if you only need 2 inputs. I hope it works for you.