The full RepoBee user guide is heavily centered on the repo administration aspects of RepoBee, which is typically the responsibility of the course responsible. As a teaching assistant using RepoBee, most of that is probably noise to you. This guide is intended to give teaching assistants using RepoBee a quickstart in its use, without having to sift through the entire user guide.
Of course, you will need to both install and configure RepoBee before you can use it. See install for install instructions, and config for how to configure it. As a teaching assistant, you typically don't need to configure the template_org_name, but it is very convenient to configure the students file for the students or groups that you are responsible for.
To correct student assignments, you will typically want to clone them to your local machine. The basics of this is described in clone_action. You also have possibilities to customize your workflow by using or creating plugins. Some of the builtins may be useful to you, such as the auto_javac plugin that tries to compile the students' Java code, or the auto_pylint plugin that runs pylint on Python code. See plugins for details on how to use plugins.
See the cli for further details on the exact options you can use when cloning with repos clone. For example, the --update-local option is very useful for being able to update previously cloned repositories.
For courses that provide student feedback by opening issues, the feedback plugin is very useful. It allows you to write your feedback locally, and then open issues for all of your students at the same time. This also means that you don't have to do all of your correcting in one go, but can do it incrementally, and still be able to easily provide feedback to all students at the same time. You can install it with repobee plugin install and then activate it with repobee plugin activate. This adds the issues feedback command, that allows you to open feedback issues in bulk. See the feedback plugin docs for details on usage.
In conjunction with opening issues on the issue tracker, it's useful to be able to have a look at what issues you've opened. The issues list command allows you to do just that. See the issues_list part of the user guide for more details on that.
Finally, you may want to clean up your issue tracker by closing issues. The issues close command allows you to do that, and you can find details on using it in the close part of the user guide.