How about something a little easier to start with? Backbone was made in Amos, but it takes all the hard work out of making the games so you can get straight into designing levels, characters, stories and challenges!
Here's a review of Backbone that Rebel wrote a few years ago, it describes how you can use Backbone to make different kinds of games:
http://www.amiga.org/forums/showpost.php?p=396250&postcount=1Here's a screenshot of the program running with as many of its windows open as I could fit on screen. Don't be put off by how confusing it looks, you generally only have two or three windows open at a time:
http://www.amiga.org/gallery/images/5087/1_Backbone.pngWith Backbone you can create platformers and run & guns like Ruff & Tumble or Superfrog, as well as overhead shooters like Alien Breed or The Chaos Engine.
You can download Backbone for free from Aminet here:
http://aminet.net/package/dev/misc/Backbone_Full http://aminet.net/package/dev/misc/Backbone_Upd http://aminet.net/package/dev/misc/Backbone_KeyExtract the Full archive and install it first, then extract the Update and install them over the top of the files from the Full archive, then extract the Key and copy it to the Backbone drawer. Now you have a fully working and registered copy of Backbone installed, and you can make games with ease!
Backbone needs an Amiga with Workbench 3.x installed, and benefits from faster CPUs. I wouldn't recommend trying to run it on an A500 unless it's upgraded. Games made in Backbone can run from a CD on a CD32 though, so you can publish your own CD32 games at least!