You can add Marking Periods through the following steps:
  1. Go to Academics 
  2. Grades > Select Grading Setup 
  3. Select Gradebook Settings 
  4. Use the School Level drop down to select the appropriate School Level
  5. Select Add Marking Period or select the 3 dots beside the term
  6. Enter in the appropriate information and select the preferred options for Access
  7. Save changes