How to model both the legs of a human at the same time? (beginner)

I am a beginner and I’m reading a book about Blender, in italian.
I am trying to create some figures as exercise but when I watch to YouTube videos I see that people can model the human figure in the front view in a symmetrical way. So, when they move something on a leg, it is the same on the other, for example.
How can I do it?

Thanks in advance!

Option 1 - Delete half the model and add a mirror modifier
Option 2 - In edit mode in the ‘Options’ tab of the toolshelf there is the X-Mirror option