Stat Checks are exactly what they imply: rolling equal to or less than your stat. The GM will add in difficulty modifiers for how difficult the action is though. For example, lifting a heavy piece of metal would be a Body Stat Check; you have a body stat of 8, but since it’s a huge piece of metal, the GM deems that there be a difficulty modifier of +2 to your roll. Originally you only had to roll an 8, but with the +2, your roll will be increased by 2, meaning that you have to roll a 6 (if you rolled a 6 or lower now, 6 + 2 = 8). Always be sure to add the diff. modifier to your roll at the end.