I'm a student rather than an instructor, but figured I can answer the question just as well seeing as I started out by doing a trial flight!
1) My instructor showed me the checklist and explained he was going to run through it, but didn't read every item out to me and show me exactly what he was doing on each one. Actually, given that I was paying for the trial flight myself, and was using it to check out the school rather than see whether I wanted to proceed onto my PPL, I'd have been happy for him to talk me through it in more detail.
2) Yes he did a safety briefing - explained about the fire extinguisher, how to get canopy open, etc. etc..
3) No, I wasn't given the option to do any radio calls. I didn't do them for my first few lessons, either - and I actually quite liked being able to just concentrate on the flying to start with. Just listening to the radio was enough of a novelty for the trial lesson. Although, I imagine I would have enjoyed just being given a couple of things to read out!