Depends on how you like to learn. I'm a doer so I just got stuck in building and bodging things together.
Plenty of videos about, Jeff Geerling (youtuber who does lots of Raspberry Pi stuff) has a bunch of videos and a book.
Well worth it though. I couple it with terraform to handle the infra stuff and I can have a basic VPS spun up with a locked down firewall and SSH with a single command and about 5 minutes.