Depends on the gym & coaching staff, but I can speak to how my first class went;

An older former kickboxer works there as the instructor, and initially he demonstrated proper form & striking technique (boxing only, no kicking until a few weeks in), and then just let us hit the ropes (literally - we didn't hit the bag or pads initially; he told us to just hit the climbing ropes just to get the feel for distance & shit before moving on). He then left to hit the heavy bag and would check on us occasionally, correct us & answer questions.

So we did that, some cardio (jumping rope, running, I did some pushups & other bodyweight exercises too..), no sparring or anything. Just started super slow & chill. It was good.