show do i set up airport express base station

You posted under the heading of "Extending the range of your wireless network....".

Is that what you are trying to do?

Will the AirPort Express connect using a wired Ethernet connection.....or connect wirelessly?

What is the make and model number of your "main" Apple router?

What operating system are you using? If you have a Mac, and do not know, click the Apple icon at the upper left corner of the screen, then clidk About This Mac. Post back with the OS X Version number that you see there.