|Only one should be set up as an extender. You need an existing wireless network to be able to extend it.|
So lets say your linksys is the primary router and is connected to your internet. We'll also say you have the wireless network on it enabled (secured with encryption too) and working. You would then configure the "extender" feature on the other piece of equipment and connect it to your existing wifi network.
As to how exactly to do this, read the manual. Pay close attention to the part dealing with the extender feature.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.