Just to make sure we're on the same page, we're installing the patch found
here. Everything should be compressed inside of a ZIP file.
When you open the ZIP file using Window's File Explorer, you'll see a folder named "Arenas". It is this file that needs to overwrite the "Arenas" folder in your RA2 installation (it won't remove any of the Arenas that you have already installed). It is a common mistake for people to accidentally install the Arenas folder of the download inside of the Arenas folder of RA2 or not allow the installer to overwrite the existing folder. Let me know if this doesn't fix things for you or if you need any clarifications.
The showcases are for people to improve and inspire others. It doesn't really matter how bad you are because you'll undoubtedly improve. That said, you wouldn't have to make a showcase if you don't want to (I never did). There are other benefits to joining like faster responses and the ability to join tournaments/contests. GTM is always looking for new members and content.
Edit: I forgot to mention that we also like to see people's ideas. In fact, we have a section devoted to taking peoples requests for RA2 mods. One of my favorite threads in that section is the
Arena Ideas thread and I, for one, have worked on implementing many of the ideas suggested there. We also have many modders that are willing to help you if you want to learn to do more than build bots.
Edit 2: I'm not trying to pressure you into anything. There is just a lot that GTM has to offer its members and I didn't want to leave out any of the big things