3 solutions, top = best
1) run ethernet cable from primary router to second router in basement.
2) use powerline adapter from primary router to second router in basement.
3) get a wireless bridge to recieve wifi signal, and then plug it into secondary rotuer.
As far as configuration it depends on your nework access/security goals.
If you want to allow them to access shared files/printers then you will want to configure the second router as an access point.
If you do not want them to have access to shared network files/printers then you will have to do some configuring. Your options vary depending on what options your router has, and if your router can be upgraded to dd-wrt or not.
Some routers allow you to set access restrictions...