After you plug in your webcame, the output of the following command should not be empty.
# ls /dev/video*
/dev/video0
sys-apps/usbutils provides lsusb.
See if your hardware is detected, e.g.:
# lsusb
Bus 001 Device 009: ID 046d:08d9 Logitech, Inc. QuickCam IM/Connect
For most USB webcame, make sure the following kernel options are enabled:
CONFIG_MEDIA_CAMERA_SUPPORT
CONFIG_USB_VIDEO_CLASS
evice Drivers --->
Multimedia support --->
[*] Cameras/video grabbers support
