Originally Posted by brntcrsp
Some routers can be configured as access points too.
Good call. In fact, most of them can. Just turn off the NAT/Firewall options.
Originally Posted by mirkazemisaman
Can a wireless access point be connected to an existing network wirelessly or do you need to use ethernet cables?
There are wireless-to-wireless bridge setups, but they're rare. They assume that you already have one AP, of course. If you don't have any APs yet, then no, the first AP must be hardwired into the network. (How else would you do it?)
compose an entirely-wireless network and use the AP as a base station. It's less important in that case, as you could also use Ad-Hoc networking (although an AP typically provides some more security options than an Ad-Hoc setup).