If your course has been integrated with an LMS platform such as Canvas, Blackboard, Moodle or other LTI enabled platforms, you will access Codio through your LMS and you will automatically be added to the relevant Codio course.
If you are not using an LMS then your instructor should provide you with one of the following ways of joining.
A Student invite URL you can click on to join the course.
A two word token you can enter in the Join Course dialog that comes up when you click Join Course on the Codio website. If you already have a Codio account you can also use the Join a Course in the Study section of your dashboard.
You can log into Codio to work on assignments that you have already begun, after completing the above process. You must start new assignments (labelled ready to go) by accessing them through your LMS system.