A "Carbon Footprint" is the measure of the total amount of greenhouse gases (usually expressed in carbon dioxide - a poisonous gas) emitted as a result of all your daily activities. From driving to work, using the computer or any other appliance, or even taking a vacation will cause you to contribute to the burning of fossil fuels, which is what provides direct or indirect energy to support human activity.
Think about it...what is your favorite object in the whole wide world? Let's say it is your cell phone...now think about all the parts that make that cell phone work (fuel was used to make these)...think about how many miles each of those parts traveled from the place that it was made (could be as far as China), then all the way to your local store in Hawaii someplace (fuel was used all throughout the transportation of your phone) - even after you purchase it and each time you charge it up (using energy, which in turn uses fuel) contributes to the carbon footprint. Well, buying that cell phone is just a minor example of how you, and all of us contribute to the carbon footprint...now think about everything you do daily, everything that we buy, consume, toss-out! It's obviously difficult not to contribute to the carbon footprint, but just being conscious of our actions by not purchasing unnecessary objects, by walking, or riding bike places instead of driving, by taking a bag with you to the grocery store instead of using plastic bags, etc. - just adopting one of these can reduce your carbon footprint significantly! So what are you waiting for?