Three ways to add students. Take your pick.
1) Type them in directly. You're only required to give them a unique user name, although you probably want to type in their first and last name. No password is required.
2) Auto-Generate accounts. If you click on this button, it will ask for the number of accounts and a prefix. If you type in 30 and A, you'll get A1,A2, A3..A30 for usernames. You will then likely want to go back and fill in first and last names.
3) If you have an existing CSV file (excel spreadsheet) containing student names, you can do some slight modifications and upload it. More directions on this method here. If you've done a CSV upload before this will probably make sense, otherwise feel free to contact me: 425-312-3363 | firstname.lastname@example.org
I think #2 is quicker than #1 but it means you are okay with the simple user names assigned by the Teacher Portal. #3 is the quickest IF you've done CSV uploads before, otherwise it's a (worthwhile) learning curve.