These two icons will manually change the amount of indent that you use in your formatting, either decreasing the indent(moving the content in the selected area farther to the left) or increasing it(moving the content in the selected area farther to the right). The button with the arrow toward the left is decrease, and the arrow on the right is increase.
Here is some indented text.
Here is some even further indented text.
You can indent lists to create subbullets to organize in an outline style.
***NOTE*** The Tab button on the keyboard does NOT create indents.