I am still new to this. But is there a way to see how Clients can add new Content to the CMS? Do I need to have the starter plan for that?
No you don’t need to start a plan for that, you can preview what content creator mode looks like by going to the view menu and toggling content creator mode from there. Here is more documentation on it. https://docs.plasmic.app/learn/content-creator-mode/
If you are asking about the plasmic CMS instead, which is for structured data, you can look here https://docs.plasmic.app/learn/plasmic-cms/