There's actually a few ways to build UI in Unity: IMGUI, uGUI (aka Unity UI), and UIElements.
IMGUI is primarily for Editor UI, thus I assume you probably aren't very interested. I haven't worked with it myself, so it would be pretty presumptuous of me to give tutorials on this one.
Unity UI is the current standard. As I'm not really sure what part of UI you want covered, I'll just give a general set from one of my favorite Unity tutorial video makers:
as well as one for a start menu specifically in a more artistic style (though it also covers simple animation for buttons)
I think all of these (except maybe the pause menu) can apply to other types of projects done through Unity as well, but it's primarily for games, being a game engine and all. This is all pretty basic stuff, though, as you can get super advanced with particles and scripting and all that jazz.
UIElements is an upcoming feature (implemented in 2019.2, but not feature complete yet) that essentially allows developers to use CSS in an active building environment. This is poised to be the standard for UI in the near future. Here's a pretty thorough demonstration of the workflow from Unite Copenhagen 2019 where they replace a barebones UI setup using UIElements.
You can find documentation for all three of these here in case you are curious during any of the videos as to how something works, specifically.
