To me, a branch is a version of the source code. There is always a main branch. You cannot delete this branch. Each commit updates the branch with your changes. If you're working with others, you can make a copy of this branch and later, when you're done, you can merge that new branch into the main branch.
In the Mendix IDE Studio PRO you can see branches under Version Control / Manages Branch lines.
You can see branches in the "Branches" section of the Mendix Studio Pro application. To access it, open your project in Mendix Studio Pro and click on the "Team Server" tab. From there, click on the "Branches" button, and you will see a list of all the branches that exist in your project. You can create a new branch, switch between branches, merge branches, and delete branches from this section.
It's important to note that using branches correctly is crucial for maintaining a healthy and efficient development process. You should use branches to isolate changes, test them thoroughly, and only merge them back into the main line of development when they are ready.