Crackmes are how I got into it. crackmes.one has a bunch of good ones. I whipped up a quick and easy one here for you you can run it if you want but it doesn't need to be run (generally don't run random executables you download off the internet) just load it in ghidra/radare/<decompiler of choice> and figure it out. it's just about finding the main entry point of the program and following the flow. https://filebin.net/h4kp7s0z04kqa5om