You need to set your tabs and set the "Leader". To open up the tab palette, hit apple+shift+T or go to "Type" --> "Tabs"
Set a tab to a right justified tab then on the ruler that you see in the Tab palette, position it where you need it. Put in your leader character in the approprate field and you're done.
If you did this correctly, if you hit "tab" on your keyboard, the cursor should jump to the right side of the text box with a string of "." right behind it.