If you haven't submitted using Microsoft Teams before, follow the steps below:

Move to the Teams section of the side-bar and select the Team used for your course.

Alternatively, go to the Assignments section and navigate to your assignment from there.

Navigate to the Assignments tab.

Open the assignment you would like to submit to.

Move to the My work section and select the + Add work button.

Add the files you would like to be checked. 

 Use the Turn in button to submit your files.