These are useful for keeping track of where customers are coming from and to measure your returns on your marketing spend. They are available on the 3rd step of customer creation.
To add marketing type in your office, Please see the steps below:
Step 1 - Go to settings > types > marketing types
Step 2 - Add Marketing Type
Step 3 - Fill out the name and description and make sure to click "enabled" to make it visible on your settings. Then hit "create".