EEnoob

Build a little inverting amplifier from op-amps. It's fairly easy once you get over the learning curve of looking up the datasheet to get pinouts, knowing what to connect where, making the connections *to match your design* (protip: you'll fuck this part up more than once).

Once you have it built then try rewiring it to make it non-inverting, then differential. They're easy modifications.

Once you have a basic grounding (pun intended) from doing this then try building a power supply - this is a rite of passage for most electronics hobbyists and there are loads of guides online for different kinds depending on what bells and whistles you want. It's a bit of a catch 22 in that you'll probably need to buy a power supply first to be able to build and test one...