You can either join your existing network and allow your original router to control everything or use the airport software and base station settings to create a new network. Assuming you have the new AEBS you can create wireless networks using variations of wireless protocols e.g 802.11a/b/g, 2.4Ghz n only, 5 Ghz n only or 2.4 n with g compatibility.
All the possibilities are listed in the Apple documentation for the AEBS and on line.