To align or evenly distribute objects, select them and click on the Align objects button 
on the object-specific ribbon tab.
Note: An object-specific ribbon tab appears on the far right as an additional tab when you select an object.
If only one object is selected, you can use the command Align Objects to place the object left-aligned, right-aligned, at the top, bottom or centered on the slide.
If multiple objects are selected, the command Align objects will align or distribute them as follows:
▪Align left: This option aligns objects to the left edge of the object placed furthest left.
▪Align center: This option aligns the objects horizontally centered to each other.
▪Align right: This option aligns the objects to the right edge of the object placed furthest right.
▪Align top: This option aligns the objects to the top edge of the top object.
▪Align middle: This option aligns the objects vertically centered to each other.
▪Align bottom: This option aligns the objects to the bottom edge of the bottom object.
▪Distribute horizontally: This option distributes objects evenly between the left edge of the object furthest left and the right edge of the object furthest right.
▪Distribute vertically: This option distributes objects evenly between the top edge of the top object and the bottom edge of the bottom object.
The last two commands only work if at least three objects are selected.
Tip: You will also find the commands for aligning and distributing objects in the context menu by right-clicking on the selected objects and selecting the entry Align or distribute.