• Step 1: have an old laptop/computer/Raspberry Pi that you can leave on at all times. Probably install Linux on it. Specs really do mot matter, basically anything will work.
• Step 2: think about what you would want to self-host. Check here for a good list. Start out with something that is not a real problem if it does not work, like a personal wiki or notes or something. Choose a reasonably popular project so you can look up problems more easily.
• Step 3: try to install it: find step-by-step instructions and just follow them. Try to understand what you are doing. Ideally, use Docker containers for easy and reusable things.
• Step 4: use it and see what happens!

Check the lemmy selfhosted community (or shudder its Reddit equivalent) to get some feeling for the community.

Realistically, it will need to be a new hobby. You need to get into it and be confident that backups, etc., are well done. Especially for sensitive stuff like passwords and pictures.

'Simply' following an online guide blindly basically guarantees you will lose your passwords at some point to a crash or something.

This is definitely it. I am tall (1.94 m) and in proportion, and my equally tall friend who is skinny gets all the tall-person jokes when we go somewhere together.