You can work with and arrange the objects on a slide in a number of ways:
Layer (or stack) objects to create the appearance of depth
Group objects to more easily move, resize or rotate them as a single unit
Lock objects to avoid inadvertently moving, modifying or deleting them
Drag an object so it overlaps with one or more other objects.
In the Format 
sidebar, click the Arrange tab.
With the object selected, do one of the following:
Move an object one increment at a time: Click Forward or Backward.
Move an object to the very front or back of the stack: Click Front or Back.
You can select multiple objects to layer them all at once.
Tip: You can open the Arrange controls in a separate window that you can move anywhere. Choose View > Show Arrange Tools (from the View menu at the top of your screen). You can also add buttons to the toolbar for Forward, Backward, Front and Back.
Group objects: Select multiple objects, then Control-click one of the objects and choose Group from the shortcut menu.
Ungroup objects: Control-click the group, then choose Ungroup from the shortcut menu.
Tip: You can add buttons to the toolbar for grouping and ungrouping objects.
When an object is locked, you can’t move, delete or modify it in any way until you unlock it.
Click an object to select it or select multiple objects.
Do either of the following:
Lock: Choose Arrange > Lock (from the Arrange menu at the top of your screen).
Unlock: Choose Arrange > Unlock.
Alternatively, select one or more objects. In the Format sidebar, click the Arrange tab, then click Lock or Unlock (near the bottom of the sidebar).
Tip: You can add buttons to the toolbar for locking and unlocking objects.
You can also overlap, group and lock objects in the object list.