Select the objects you want to align. How?
Right-click any of the selected objects and select Align. The alignment options are Top, Bottom, Vertical Center, Left, Right, and Horizontal Center. Select one of the options.
The objects are aligned according to the option you selected, and the object that you selected last.
TIP: The object with the white handles controls the alignment that is applied to all objects. If the object you want all other objects aligned to is not selected, click again on that object (all other objects will stay selected).