The purpose of this kind of sketch is just a warm up exercise. Your focus is on the rhythm of the model's movement, the flow of the lines through the body. It's only three minutes so you won't have time for many details.
There are many approaches to gesture drawing, some artists are very scribbly, some use a big chunk of charcoal and just block in shadows. Some focus on just one portion of the body like an arm or leg while others like myself try to get as much of a drawing done as possible. That last one may well be the wrong approach, but it's tempting because gesture poses are usually the most dynamic and interesting and I want to draw those more than any others.
You'll notice as we go along that the majority of my sketches are of women sitting. That's because 90% of class time we draw women just sitting.
Fortunately for me many of our models welcome me to take photographs. If I am fortunate enough to get a good photo of a nice pose I'll sometimes continue working on that sketch at home and may eventually get a very nice finished drawing from a gesture. This experience is vastly inferior to drawing in person. The camera loses a lot of information that you can easily see in person. For example in the photo that thigh might just look like a solid white shape whereas in person you can discern several shifts in the surface of the plane. This makes all the difference in the world as to the realism of your work. Sometimes my experience can step in save me because I know there should be a plane shift there even if I can't see it. Other times not so much.
But the world does not measure us by the things we could have done if we had better opportunities nor by the quality of our reasons for the things we didn't do. The world measures us by what we do nothing else. So we do what we can with what we have. Improve on what you have if possible certainly. But if you learn nothing else in your life learn this, however much you have or however little, the importance of what we have is always microscopic compared to the importance of what we do.