So, you’ve created this platform, but how do I access or start discussions on topics othet than Diaspora itself?
This discourse instance is only for discussions (mainly development and support) about diaspora itself.
I just signed up, so how can I go to diaspora to read other stuff than diaspora itself?
This is discussion forum about the Diaspora platform: support, feature requests, issues, development, etc. You talk about Diaspora here but it isn’t Diaspora itself.
To actually use Diaspora you should register at any Diaspora pod (server) you like and log in there. Follow the instructions here. It doesn’t matter which server you choose as they all are interconnected, just pick something with the name you like, good uptime and recent software version. Then explore the network - add people, follow tags and have fun 
There will be short and easy tutorial available when you first sign in.
If you run into problems,come here into Support section and people will help.