Selecting one or more objects is a very common task when using Dia. Whenever you wish to move, copy, delete, or edit an object or change it's properties, you must first select it. You can also work with a set of selected objects -- for example, to move a group of related objects while keeping their relative positions in tact or to change the properties of a group of objects.
Selecting objects can be done in several ways, including clicking with the mouse, selecting by area, or using the Select menu to perform additional selection options.