The carbon cycle has components in the atmosphere, hydrosphere, lithosphere and biosphere.  Much of the Earth’s carbon is fixed in the short-term, while a lesser amount is able to move more freely.  You must decide if you want to focus generally on the basic carbon cycle or on a sub-component of the cycle.  Looking into the anthropogenic sources of CO2 contributions to the carbon cycle, or specific sinks and natural sources on land, in water, or cycling through the atmosphere are all possibilities.  What aspect of the carbon cycle is most important for the general public to better understand?  Or do you think people don’t know what the general carbon cycle even is?  The answer to these questions should direct your decision on area of focus.  
There are many additional information sources online and you should search for more information there.  Keep in mind the quality of your references.  Look for information from peer-reviewed science publications, universities, museums, or encyclopaedias.  Be wary of websites or sources that have hidden or open biases.  Try to also look for recently published sources.  The following source is somewhat dated, but has a good review of the complete carbon cycle and comes from a reputable source.  It will be an essential source of information to use in your infographic.
Once you understand the carbon cycle and decide your focus for your Carbon Cycle Infographic, you must gather some data.  Are you looking for values on the distribution of Carbon around the globe or in a particular sphere?  Are you looking for how the numbers are changing and where carbon is moving from?  Whatever your goal, seek out the best data and find reliable numbers.  Make sure to list your references at the bottom of your infographic in small font, if you are using additional sources