As an admin for a Non Profit account, you have the ability to add additional users. You can do so by logging into your organization's account and selecting the Settings tab.
Then select the option to Add or edit users
Scroll over to the right-hand side and select +Add new user
You will then be prompted to enter the new user's information.
Once you have entered all required information you will then select Add User. The new user will receive an email which will prompt them to complete their login credentials by setting up a password.
Please be sure to have them check their junk mail or spam folder for this email.