To get the gist of something, it is to understand the main point of whatever is being discussed.
For example, a person may be telling you the plan to buy cake, and they tell you that they have to go in, choose, and buy the cake. You understood that part, the main point, and then the person goes on to tell you the in between points that tells you the details of their plan.
Get the gist of it means to write a short summery in 10 words or less, to give bullet points of major events that have happened and to tell what the text is about!
