A router containing a WLAN interface has an additional ethernet device
representing it. On Broadcom-based hardware it is typically wlan0
or on NETGEAR WGT634U which has a Madwifi WLAN chip, it is ath0, ath1, etc.
You can use these interfaces standalone or bridged with other devices, e.g. the internal
LAN.
For AP mode and WEP/WPA/WPA2/WPA3 you need to select, configure and run hostapd.