Focal length is something I believe most hobbyist photographers can get away without knowing too much about. Especially those who never move beyond the kit lens. I don’t think it’s necessarily essential knowledge, and given the choice between learning it or going out shooting somewhere, I’d probably advise the latter.
The differences in your pictures caused by different focal lengths should be obvious to the naked eye, and you’ll know when you’re shooting what looks good and what doesn’t. Even if you don’t know why.
Having said that, an understanding of focal length is good to have when buying lenses, or simply wanting to know how zooming in alters your photographs in ways that simply getting closer to your subject doesn’t.
This then is a comprehensive yet simplified explanation of what focal length means for photographers. It explains how it affects your pictures without drowning you in science.