There's so many things you can learn from! Since you mention wanting to improve how you use Emacs for development, a couple of features that I use everyday and feel very "emacs-y:"
- compilation-mode (`M-x compile`) - It defaults to a `make` but the resulting buffer is useful for any sort of build/compile/test job that you want to spawn. For example, I'll use Projectile's `projectile-test-project` command (`C-c p P`) to quickly run jest tests for my TS projects:
https://i.redd.it/xyte0s83if3c1.gif
- occur - (`M-x occur`) I use this mostly as a persistent search buffer. Basically, you can list lines that match a search string and then follow and/or visit them in the corresponding buffer. I like that the numbers in the occur buffer give you a rough idea of where the search term is in the original buffer. Pressing `n`/`p` in the occur buffer advances to the next line as well as gives a quick highlight in the original buffer.