There's nothing really at all that you need to know prior to using the Supro Model 50, even if you aren't all that experienced with guitar amplifiers. The only parameters that the amp has to work with are for tone and volume, which should be self explanatory (if there aren't you might want to try doing something else with your time). A manual won't be necessary nor readily available for the Supro Model 50.
For such a little amp, the Supro Model 50 has a pretty big sound. It's not going to knock your socks off, but there is certainly some get up with this little guy. It doesn't have much versatility, but the sound that is possible is warm, full and quite clean. If you turn the amp up all the way or approaching all the way, you'll get just a little bit of overdrive from the tube. I've used the amp for recording only with a Fender Telecaster, Stratocaster, and Les Paul guitar. We used this amp for some clean/slightly overdriven rhythm guitar parts on a recent recording session that I played on and engineered.
While at this point pretty rare, if you can find the Supro Model 50 it's a great little amp. Again, I'm not sure exactly when the one I used was made, but it's got a really vintage look and sound to it and is definitely pretty old. I don't know too much about the brand Supro either, so I don't have much to compare it to in terms of their other amplifiers. I do know that the Model 50 is a must try for those who come across it...