You are not the only one with that problem. I was also confused that configuring channels, tags and categories is not located in the admin area like for example badges are.
While you can also only customize groups from the groups page, there is at least a link in the admin area taking you to the group page.
Maybe something like this should be added for the others as well.
If you haven’t done it before, it’s also worth looking at the topics in the Documentation > Site Management category. At the beginning, the #getting-started tag, which shows the most helpful topics, is very helpful.