I done a more general handyman course (plastering, plumbing, tiling & woodwork) a couple of years ago, one element was plumbing which covered the basics of how the various systems work. On the practical side we planned & fitted a mock bathroom and installed and then pressure tested a radiator, we done it on the old fashioned way using copper pipe work & soldering etc…
I tried a short stint of doing some private jobs but found that I was nowhere near experienced enough to tackle some of the jobs. I think you ideally need some on the job training with an experienced plumber rather than going straight from a course or college.