What are .ko files

What exactly are .ko files? They seem to be related to modules but aren't actually modules since insmod won't load them. The question arose because I'm trying to get a PCTel internal modem to work. I have two files, pctel.ko and ptserial.ko, in my /lib/modules directory (a couple of levels down). I would guess that those files contain the modules I need, but how do I get the modules loaded? I did lsmod | grep pctel and it came up with nothing, so the modules apparently aren't there yet. Paul