Depending on how you’ve configured the Mass Update buttons, your users will see the button appear if they satisfy the security requirements. See an example below:
When selecting one or multiple rows with the standard Salesforce.com checkboxes in the search grid, the Mass Update Edit page appears. The fields that appear are those selected from the defined field set:
Whether selected in the Field Set or not, the Object Name field will always appear as the first column in the preview grid so that you understand which records your editing.
It should also be noted that by checking a box next to a field but leaving the value blank, that is instructing the Mass Update Tool that you intend to have that field be set to null.