Since the FAA doesn't publish a logbook, I'm guessing you mean the Jeppesen Professional Pilot Logbook, the one with the green pages. The only things you have to log in the US are training flights for a rating and enough flight time to meet the requirements for ratings and enough flights to show currency. The logbook has headings at the top of most columns with some blank if you are flying something strange - I labeled one column "Balloon." Some pilots log hours and minutes but most US pilots log hours and tenths of hours, there are charts around to convert minutes into tenths if that is the way you want to log time. I remember 40 to 45 minutes was .7.