As it's written in the doc, you have to make a "search with various criteria". Then select all the machines, click on the Group icon. A new window is opened. You have choice with a dropdown list mass affectation => for the selection, for the request. Select what you want. Next, choose between dynamic or static group, an another dropdown list is available. Choose what you want. New group in your case. Name your group and all machines will be inserted in the group.