I would suggest choose a project and start from there, one of the first things i started with on a Pi1 is KODI (old name XBMC), it is a media player / streamer with a nice interface and many features.

Emustation is also a nice project to run on a Pi, it has Emulators to play the old school games, and also comes with a nice interface.

There are also a few projects to turn a Pi with USB webcam into a security monitor

Or install Raspbian OS (desktop) and use it for simple tasks. and try do some custom things with the OS.
(make it into a file server)

My NES Label Slider project is also not so difficult though you will need a 3d printer for the housing of the Pi, it involves a little programming is easy to following and gives a idea of how to convert in this case Raspbian OS into your own project.
https://steemit.com/gaming/@techtek/digital-nes-label-slider-tutorial-everything-included-to-make-your-own

After some time you maybe want to buy one more because you like to play with them and want to keep one in a project and have a extra one to play with :)

Thank you for your reply