Hopefully it is turned on, otherwise you would probably fall from lack of balance. Second since it is a dirt bike I hope you are in soft dirt because it seems you are a beginner . With it running you pull in on the clutch, that's the lever on the left side handlebars. While you have it pulled in take your left foot and press down on the gear shifter, slowly release the clutch and give it a little gas, that's the right side handlebars that the handle can be moved backwards and forwards. when you get moving pick your feet up and place them on the pegs. When you feel comfortable with what you are doing pull the clutch in and with your toes under the shifter pull up on it, you are now in second gear, give it a little more gas so you don't bog it down and kill the engine. Hold on tight and repeat with the rest of the gears all the while giving it more gas so the ride is smooth. That's all there is to it. Keep working at it.....CLUTCH-SHIFT-GAS-CLUTCH-SHIFT-GAS and so on.
Good luck