It's not hard to know what actions impact CO2 production. Like nosianu else said, just stop taking carbon fuel out of the ground. Anything above ground is part of the carbon cycle and is fair game - manure, trees (to a point), etc.

But I think what's hard about this is not understanding what causes CO2 production, but understanding what it means to stop burning buried carbon fuel. It means no more computer, cel phone, cars, no flying, no 2-day shipping for [ANY PRODUCT!], no container ships and planes shipping food and products all over the world. It might mean abandoning air-conditioning and having to hand-wash your clothes. It means abandoning modern comforts (not necessities). It means abandoning a hyper-consoomer lifestyle and becoming more localist, which most of us simply cannot fathom doing.