Adding an FTP user is great if you want to give out access to a specific folder on your server, without allowing access to the full server. It isn't however recommended to create multiple FTP users all accessing the same folder (such as your main site root) as this can cause lots of permissions issues. It is recommended in this instance just to use one single FTP account - you can always reset the FTP password each time you've finished accessing it.
To create new/multiple FTP users, please follow this guide.
1 – Login to your Cpanel
2 - Click on Account Information
3 - Click on List Accounts
4 - Click on the domains CP button that you want to create an FTP account on.
5 - Click on the FTP Accounts button.
6 – Enter the details of your new FTP user. Make sure you use a nice and secure password - random letters, digits and symbols - this is very important as it is part of your site security. Select the folder you'd like the FTP user to have access to. You can create a folder via FTP using the master account first if required. Click 'Create FTP Account' to create the user.