Hi @Daniel Lopez5. Let me first explain when we show the [+] button on top of the community:
By clicking on the [+] button, you can pick which content-type you would like to use to share something in the community (Questions, Post, Discussion, Article). Also, you can "Create Group" from this section.
However, if you have only one content type9 enabled in the community, and the "Groups12" app is NOT installed in your community, then, the [+] button will be replaced by the "Post" button that simply allows users to post something in the community.