In general, if you can avoid having to build a UI (User Interface), do that. Making UI's is quite difficult and a lot of work, and there might be some packages available already that can do this for you (e.g. see Unity Experiment Framework)
If you're going to build a UI, you have 2 options:
- The legacy UI toolkit: More documentation & tutorials on this & relatively simple to get into. However, when the UI becomes complicated/needs to scale across different devices, this method is not very flexible.
- The UI builder: a new way to build UI's in Unity using CSS like formatting. Very powerful and nice to use, but kinda finnicky and currently still in preview (so things are changed around quite often). Harder to get into, but a lot more scalable to more complicated setups.
Some resources to help get you started.