Within your Software's Main Menu > Go to Company Contact Setup
In Company Contact Setup Scroll down > Click on Add Contact
👉 Add in their Contact information

Make sure you select "Allow Multiple accounts to use this" for the Email address and Cell Phone Number to avoid future errors.
👉 Provide them with their unique Username and any password.
👉 Add a check for "must reset password on first login"
👉 Click on Continue.
You can now provide them with the login credentials.