What does 'one click booking' mean?

1. Go to Settings > Activities > Add activity (time-based).

When the activity session is selected you will go to the next stage of the booking process if this setting is set to yes.

If this setting is set to no you will have the option to select multiple sessions from the dashboard calendar. 

Functionaly, you can accomplish the same with this setting either way, if it is turned on you would just select the first block you wish to book, and can then pick the duration (where applicable), with it turned off you can select the number of sessions from the calendar by clicking all of them.