Hi there, I hope you're not getting too confused!
Your floppy drive most likely has dirty heads as nearly ALL old computers will when you buy them after years of not being used and maintained. All of the Amigas I have picked up over the years, including many online friends who have also picked them up have all suffered from the problem of the disk drive not reading disks properly. Sometimes it will load part of the game or program, then fail, or show an error message window if it gets as far as Workbench, and sometimes it will simply fail early and go back to the Kickstart screen or Guru. The problem is always dirty heads in the floppy drive.
The solution is to use a simple, inexpensive floppy drive cleaning kit, which you may be able to find at an office supplies store locally, or you can get them at online shops and eBay. They look like a floppy disk with a white cloth pad inside instead of a disc, and often come with a little bottle of fluid which you put a few drops of onto the pad before inserting the disk in your drive. You would then repeat it a few times, either by re-inserting the disk or by rebooting (with Ctrl+A+A) a few times so the head gets a good clean.
Then all you need are some games. You won't need Workbench to play the games, but you should still get a copy anyway.
I'm not sure how to make ADFs from WHDLoad images but it's probably possible somehow, they're both disk images.