The router os documentation is (usually badly, in the sense of incompletely) written by very knowledgeable and smart engineers that assume that the reader is already very familiar with networking concepts. Very rarely something is explained, the router os documentation tells the bare minimum needed to do something in the Mikrotik scripts/configuration. Probably it is not the right scope for a os documentation to be also a networking tutorial, but the good Mikrotik guys are particularly tight-fisted when It comes to practical examples.
So it is a good resource if you are already familiar with basic networking and know some of the Mikrotik jargon, but It will very likely confuse you if taken as a networking learning resource.
You will find better learning material here on the forum, if you like to learn from examples.
If you instead prefer to learn theory of networking, you should look for Linux networking material, since Ros is using - even if sometimes using different names and with slight differences - the Linux network approach.
The things I wished to know when I started fiddling with Mikrotik stuff I wrote here: