Click on Assessments on the left side menu to view your assessments. To narrow down your assessments by what classes they were assigned in, you can use the drop down menu above the list of assessments.
Click the row of the assessment you wish to start. A pop-up will show you your teacher's instructions for the assessment. Click Start.
Once you've begun, you can view any attachments your teacher provided by clicking on them under Teacher Attachments. Your rubric is below that, and any Google docs that may have been shared by the teacher are beneath the rubric. You can attach your own documents at the bottom, and submit there as well.
Once you are ready to submit your work, you can attach it with any of the attachment types on the main assessment screen. For just a text editor, click the text cursor icon.
When you are ready to submit your work, click Submit Assessment. Keep in mind, once you click Submit, you won't be able to go back and change your work, so make sure you're ready!