Place in front of the vehicle's front or rear tyres in a pair (never use one ramp alone). Ensure the ramps are straight. Kick the ramps under the tyres to decrease the chance of them sliding. Slowly drive the car up the ramps. Listen for the sound of the ramps sliding. Stop and try again if either ramp slides - they must remain even. At the top of the ramps, you will feel the vehicle drop down into the top. Do not drive further, or severe damage to the vehicle may result from driving off the top of the ramps. Have somebody guide you.
With a manual transmission, you will likely need to ride the clutch a bit to get onto the ramps at a not-excessive speed.