Asterisk Channels 101

This is probably not the most sophisticated question and might be obvious, but after googling and reading docs for days I’m still unclear what things like the Asterisk Manager mean by “channel.” For instance, the “Action: originate” command needs two things, an extension to dial and a channel. But the only time I see channels is between established calls. Most times in “originate” examples this value is something like “SIP/100”. But I try originate with “SIP/”.

Same thing goes for conference calls. I have meetme setup and working in my dialplan, and I can take an existing call’s channel and use redirect to send that to a context that puts you in a certain meetme room. But how can I redirect the channel of a phone that isn’t in a call (i.e. doesn’t have a channel)? Is there some way I can use originate to send a device/softphone to my context and extension that handles conference calls?

What am I missing?

Channel is used in two senses. For circuit switched interfaces, they are largely degenerate, and I suspect that is how they started.