Your carbon footprint is a measure of the greenhouse-gas emissions you produce in your everyday life. Your total carbon footprint is divided into two parts: your primary footprint, which is the emissions you directly cause (by using the stove, driving your car, running up an electricity bill, and so on), and your secondary footprint is made up of the indirect emissions which are a result of your lifestyle choices (eating at restaurants, going to the movies, buying a lot of clothes or electronic devices, etc.).
There are plenty of websites that can calculate your (primary and/or secondary) carbon footprint for you, but you have to provide some details first. For whatever period of time you want to measure (a month, six months, a year) you have to know your energy bills (gas, electricity, coal, propane, etc.), the number of miles you’ve traveled in your car and by public transport, and any airplane flights you may have taken. This information all contributes to your primary footprint. The secondary footprint is more approximate and requires you to input data like how often you eat at restaurants, how often you buy new clothes, and whether/how much you recycle. Once you know the value of your carbon footprint, you can see all the different factors that contribute to it and look for places where you can cut back.