Well, not exactly. This is a very simple treatment of a very complex subject, but I hope that I have given you a basic concept of how tubes work. Now for the practical knowledge I promised. The driver tube is the small tube closest to the bigger power tube. It will be a 12AX7 or 12AT7 depending on the model.
Good tubes can sound like ass without a new driver.
Also, if you have matched sets and it's an amp with four power tubes, make sure one set is on the inside and one on the outside, not one set on the left and one set on the right. Next, fire up the amp and have your friend play guitar through it. Turn it up to the loudest you usually play it, and have your friend really lean into it. Now, from behind the amp, look past the power tubes in between the transformers for a small hole. This is the bias adjustment pot.