linuxmemes

The other poster gave you a lot. If that's too much at once, the really low hanging fruit you want to start with is:

• Choose an active, secure distro. There's a lot of flavors of Linux out there and they can be fun to try but if you're putting something up publicly it should be running on one that's well maintained and known for security. CentOS and Debian are excellent easy choices for example.

• Similarly, pick well maintained software with a track record. Nginx and Apache have been around forever and have excellent track records, for example, both for being secure and fixing flaws quickly.

• If you use Docker, once again keep an eye out for things that are actively maintained. If you decide to use Nginx, there will be five million containers to choose from. DockerHub gives you the tools to make this determination: Download number is a decent proxy for "how many people are using this" and the list of updates tells you how often and how recently it's being updated.

• Finally, definitely do look at the other poster's notes about SSH. 5 seconds after you put up an SSH server, you'll be getting hit with rogue login attempts.

• Definitely get a password manager, and it's not just one password per server but one password per service. Your login password to the computer is different from your login to any other things your server is running.

The rest requires research, but these steps will protect you from the most common threats pretty effectively. The world is full of bots poking at every service they can find, so keeping them out is crucial. You won't be protected from a dedicated, knowledgeable attacker until you do the rest of what the other poster said, and then some, so try not to make too many enemies.