I found a book by Peter McIan, "Using your Portable Studio," to be a useful resource, but I think the key to learning to use it is to experiment. You can also get an owner's manual from Tascam, if you don't have one (which mine did not) by going to their website. The 424 does have its limitations, but I've had a lot of fun with mine, and I think the best way to get acquainted with what it can and cannot do is just to set aside an evening or two to "play" with it. I mean, don't bother trying to record something for posterity---just play around and see what you can do, and get familiar with what all those little knobs do.
I would recommend a "punch in/out" foot pedal as a highly useful accesory.
Remember not to try to flip the tape over to record on the other side! I made that mistake only once. Or, if you want to listen yourself playing and singing backwards, please do turn the tape over!
Clean the heads often; happy recording!