In the Roles tab the possible entries help displays a list of the existing roles from which you can select one. You can assign a role to as many users as you like.
You can create a link with the user master record for a specified validity period by clicking on the relevant field in the Valid from or Valid to column and then using the calendar to choose a new date.
You can delete a line by selecting it and then choosing Delete.
Note that you can use the separator to move the column separators so that you can read texts that are not completely visible.