When creating groups, each group is placed in a Group Set. These sets of groups can then be used to create Group Assignments. For example, you might have:

A Group Set called Final Presentation, within which you have
Seven different groups, manually assigned or to which students signed up, and
A single Group Assignment that is assigned to every group in which they submit a presentation, perhaps as a PowerPoint file, a link to another site, etc.

The "How do I assign an assignment to a course group?" Canvas Guide covers the options in detail, but the most important points to note:

A Group Assignment is simply a choice in the Assignment options when you create an assignment, so would follow the same process you've already learned.
You can choose to assign a grade for the group or individually.
You cannot use student-created groups for Group Assignments (but you can use groups you created and had students select.
You can use Peer Review with groups, but if you want something other than random assignment of peer review across groups, you will need to assign the reviews manually.