How does an emergency tracheotomy work?

Sorry if this is the wrong forum, but I thought if I posted it here I'd definitely get a knowledgeable answer.

I watched this programme where a guy performed an emergency tracheotomy using a kitchen knife and a pen. I looked this up afterwards but what I can't seem to understand is how the person breathes with the tube in. Don't you use your mouth and throat in order to breathe?

Apologies for possible stupid question. I only did GCSE Biology!