You need to ensure that the users and group/groups already exist in smartadmin. If they dont quickly create a group in smartadmin here

1. Create and populate your csv with these headers:
   username and group. You can add as many groups as you need.
   e.g.
   username,group
   user,english-department
   user2,english-department,green-team

2. Navigate to the 'Import' section of smartadmin here and select 'Cohort Import' in the Left Hand Menu
   
   

3. You are now ready to import your csv
   
   

4. Hit the 'Upload Your Cohort CSV' Button and browse for your csv
   
   

5. You'll see a Preview of the import data to check before hitting the 'Start Import' Button
   
   

csv has now been uploaded and the users added to the groups.