Confused about muxes and channels, how long does it stay in pending scan?

I have TVheadend running to the point where the USB digital TV adapter is listed with a little green dog (I assume that means it is working OK) and when I open up "watch TV" I get the headend logo. I also set up a network (I selected the local city from the list of predefined) and suddenly a long list of "muxes" appeared on the muxes tab. But I am completely confused; how do I get channels going? The muxes all say the scan is pending. I clicked 'force scan' but that doesn't seem to do anything. Does it just take a long time? I am just trying to watch over the air digital TV. Thanks for any help!