Using auto layout I am trying to create two buttons on the bottom like this
you can done it using equal width to 2nd button like this

and the output is

Here is apple guide
You need to add one more constraint - set horizontal space between buttons to 0

You can followed the layout changes. you will get what you want.
Layout for Back button.
Layout for Go to Setting button.

You can have the equal widths constraint between the buttons, but you also have to tell them which is that width you need.
So drag from a button to the superview, add an equal widths constraint. Then in the properties of the constraint you've added, set the multiplier to 0.5, this way your buttons should be on half the screen.