The technical rehearsal is so that every cue, for lighting, sound, scene change, costume change can be tried out. At this point neither the actors or stage management will have been able to work with the set. The actors will also have all the props they need, rather than the 'stand in' ones that they would have had in the rehearsal room. A technical can last all day, into the early hours of the next day, and in some cases they can drag on into the next day with a break in between, but this is rare. It depends on the complexity of the play. Obviously the more cues, of whatever type, the more stopping and starting there will be. At the end the director will give notes to all concerned, in particular stage management will have to deal with such things as doors sticking, wobbly flats, and a whole host of things, before the first dress rehearsal. Sometimes the first dress rehearsal can follow on almost immediately after the technical, and then one final dress rehearsal the afternoon the play opens. This can be incredibly trying and when stage management have been working since the final performance of the previous play on, say, a Saturday (which was how we worked when I was in rep.) and the next show opens on the following Tuesday evening, that's a good four days solid work with very little sleep.
As with any show, the prompt corner is the operation centre who the whole show. Whoever has been 'on the book' during rehearsals will now be in control here. The 'Book' will, by now, be made up with all the cues market in. If a line spoken by an actor is the cue for, say, a lighting or sound effect, then the 'book' with have it market in clearly. In most theatres there is a cueing system using lights, rather like traffic lights in the street, but obviously a good deal smaller. You give a warning that a cue is coming up for the operator, usually a red lights, and when the cue comes, you give a green light. At Ipswich theatre there was a three-light system, which had an additional blue light. The idea being that the operator of sound, lighting or whatever, would flash the blue light to indicated to the prompt corner that they were standing by. It was quite a good idea as it allowed you to be sure the operator was ready. On one occasion at Ipswich I was doing the book for one show, I forget which now, and I hadn't got the blue light from he lighting operator. I had given him the standby, but he hadn't indicated that he was actually standing by. It got closer and closer to the actual lighting change, fade or whatever and I began to panic. It just happened that the lighting board was above the prompt corner, and was accessible by a metal ladder. I had to climb up and see where the operator was, and found him asleep! I had to operate the lighting board as he wasn't awake in time to give the cue! A bit of a seat-of-the-pants situation!
If you were put on props for a show you would be expected to go out and find the relevant items listed for the play in rehearsal. I can recall trudging the streets of Cheltenham as a very green student A.S.M. I became a good deal more savvy at going into shops and asking if we could borrow such-and-such item or items, the owner of a particular shop would be very trusting that we weren't going to damage whatever the item was or even sell it. They would be given free tickets for the play, or the next one in the season, and have a credit in the play's programme. At Ipswich Theatre I remember borrowing a white linen tablecloth for a play. Unfortunately it got badly stained with something which would not wash out. We had kept the wrapping in which it would have been carefully folded for display in the store, but when it was returned it was re-folded, so that the stain wouldn't show! Goodness knows what Debenhams would have done when they discovered that the tablecloth was stained when it was opened up. I just imagine that it would have been sold in a sale or probably not put out for sale at all.