The box to the left from the ruler?

[p.numminen]

What are Left Tab, Center Tab, Right Tab, Decimal Tab, Bar Tab, First
Line Indent and Hanging Indent?

 

[Luc]

Hello,
This is the place where you choose which sort of tab/indent you will use on
your text, once you have chosen the type of tab click on the ruler to place
it, press the tab key on your keyboard to use it. Same thing with the
indents. If you hover your cursor over the box the yellow tip will tell you
what you are choosing when you click.

 

[CyberTaz]

Extending on Luc's reply, you might want to take a look at:

http://word.mvps.org/FAQs/Formatting/SettingTabs.htm

http://word.mvps.org/FAQs/Formatting/UsingRulers.htm

HTH |:>)
Bob Jones
[MVP] Office:Mac