Free time means the same as Leisure time.
It’s the time when you are not at work or school and usually have no other obligations to fulfill.
You can decide on how to spend that time you have free.
Here is a chart of 12 things you can do in your free time:
We have a longer list of things you can do in your free time here: Free time & Leisure Activities and it goes into more detail with vocabulary about each of those activities.
English Teacher Resource
What do you like to do in your free time?