There are plenty of videos and tutorials online. Google "how to change gears on a bike" and you will get lots of hits. Probably look more at articles that talk about shifters on the downtube since what you have is the same type of shifters, just in a different location. There have been many good posts in this thread with good advice. The best advice, IMHO, is to try to shift in advance when you see a hill coming. Try to keep your cadence (turning rate of pedals) higher rather than waiting until you can't pedal any longer before shifting.

Another thing that it took me a while to learn in preparing for a big hill. If you down shift in the front, you can offset that by upshifting the rear cassette one or two gear. They leaves you with roughly the same cadence, but you are on the lower front ring and ready to downshift the rear.

A 27 mile ride is a great ride! Keep up the good work.