The first time that the actors will meet each other will likely be when they audition for a show. What will happen here will differ from audition to audition — with some requiring the ability to sing, dance, perform an instrument, and so on — but will almost always have people pair up and read lines together with the director. This will allow the director to gauge one’s relative acting ability and how they bounce off of another actor in conversation.
The second time that the actors will likely be together in the same room after the audition will be as a full cast. And the first thing that the full cast will do as a group will be to read through the entire script, with each actor reading as their given character. All of the actors are to be present — as scripts are sometimes given out at this point in time — along with the director and the stage manager, who will be keeping everyone on track. And because this is only a cast reading, the stage manager will be reading the actions (which will usually be in italics) of the scenes that are given in the script.
This is because the acting directions will be given when rehearsals start within the next few days following the first reading — depending on how long the director is willing to allow the actors to spend time alone with their script to delve into the mindset of the character.