create training data

[CrisMecho]

Hello could you help me?
I am learning the python language while installing this software.

I am at step 2, but I don't understand how to do what is recommended before reproducing the code:

"In this step, a training data set is created via visual inspection of images.
It is recommended to:
-generate a training dataset of at least 10 open and 10 closed inlets. More training data will typically lead to more accurate classification results.
-Keep the number of open and closed images roughtly equal (this can be done using 'skip')
-create at least two equally sized training datasets. One for the Landsat group (including 5,7 and 8) and one for S2.
Satellites can be skipped via Esc. "

You would help me a lot if you exemplify what is requested.

Thank you so much!