Delta-V is the total change in velocity that a rocket experiences for a trip. You can use the rocket equation to calculate how big your rocket needs to be do gain that delta-v.
For example, for a rocket to get into orbit requires a delta-v of 8.6 km/s. To go from there to the moon takes about 4.1 km/s. You can plug a Specific Impulse of 350 and calculate the approximate size of the rocket needed with ease.