Show a snapshot of all data present in file FILE at the time the less command was run. i.e. If new data is written to the end of file FILE after the less command was run, that data is not displayed.
Pressing F (capital f) while inside less will cause it to start reading at the previous end of the file and show any new data. If there is nothing new to read, it will just wait.
Pressing Ctrl-C (interrupt) while showing or waiting for new data will stop less reading at the end of the file and thus create a new snapshot. You can then scroll around the new snapshot or press F again.