You can pause a session by pressing the pause button represented by the following icon:
Then resume it by pressing the play button represented by the following icon:
If you choose to end the session, click on the arrow at the top left of the screen and choose from the options: Save and exit / Quit / Resume session
If you choose "Save and Exit" you can comment the session and save it. You can find this session in the “my Sessions” screen.
It is also possible to restart a program from the summary of a past session.