Add Roles to User or Add user to Role

Hi,

Can someone please share information about 'Add Roles to User' or 'Add User to Roles'. There options are there in Role relationship application Form exit bar.

I can make out that they help in assigning multiple user IDs to a role or multiple roles to a user ID. But If you choose Add Roles to User, enter user ID, select

VA for roles, it shows two options before showing Role names. Any idea when are used and what is right option there?

Please share any solution ID or document reference for more information about these options.

Thanks in advance!