It's very simple! SkyPrep actually marks Multiple Choice, True/False, and Fill-in-the-Blank questions for you! The only questions that you will need to mark are Short Answer questions.
When you are on the Dashboard of the platform, you will see a panel on the top left that says Ungraded Assessments. It will display the name of the assessment, as well as how many users there are that have pending assessments. Click on an assessment.
On the next page, you will see this view. On it will be some of the learner's information, as well as a drop-down menu used to switch between users being graded, a graphical display of the questions, a mark adjustment field, and a button that says I'm finished grading.
To mark short answer questions, simply select the question number. Alternatively, you can use the button that says Show only questions needing manual grading.
You can then use the Update score field to mark the question. Don't forget to hit Update when you are finished!
Once you're done, simply click I'm finished grading at the top.
You will now see a notification that says This assessment has been graded. The user may view their assessment score. This lets you know that you can safely move on to the next user that requires grading.