Login to cPanel and from the file section click on FTP Account
You will see a screen from which you can add your FTP account
To create your account fill the fields in the following way:
Log In: add your choosen username. the username for your FTP account will be email@example.com
Password: add a strong password or use the password generator
Directory: add a directory path if you want to limit permission for this account to only one subfolder
Quota: you can limit the disk space for this specific FTP account
Click on create FTP account to create the account. To connect to the server using FTP check this tutorial.