It is often convenient to hold views within other views. We can nest views by putting a view inside of another view. In this case, the inner view is the subview and the outer view is the superview. The relationship of subview and superview is relative and in many cases, a view that is a superview to a view it contains, is also a subview to view that it is itself contained by. It can be helpful, when animating multiple views, to group them together inside a containing superview so we don't have to animate each view individually; instead, we can just animate the superview, and the subviews will go along for the ride!
Embed in View, found in the Editor drop down menu, allows you to add one or more existing views into a new view. This can be helpful in the case where you have multiple views arranged in the storyboard, and you don't want their relative positions to be altered when adding them into another view. Embed in View will preserve the relative positions of the views to one another inside a new superview that is created.