The average distance between the planets Mercury and Venus is 36 million miles. The actual distance varies greatly depending on the position of the two planets in their respective orbits.
Although Mercury and Venus are the two closest planets on average, their orbits are not synchronous, so they can be on opposite sides of the sun from each other. At times, the Earth is actually closer to Venus than Mercury. Beyond Earth's orbit, the distance between planets increases dramatically. Mars is almost 49 million miles from Earth, Jupiter is another 338 million miles from Mars and Saturn another 400 million miles beyond that. At the far reaches of the solar system, the sun just appears to be a particularly bright star.