Victoria Crater on Mars as seen by the Mars Reconnaissance Orbiter. It is a simple crater that has been partially filled in with sand---note the sand dunes on its floor.
If you download the full-resolution version of this picture from the link on the picture, you will be able to see the rover, Opportunity next to the top left crater rim.
Careful studies of how the craters overlap other craters and other features can be used to develop a history or sequence of the bombardment on the moons and planets. Worlds with less volcanism or erosion or tectonic activity in their history will retain more impact craters since the planet formed.
Worlds with more geological or erosional activity will have newer surfaces or craters that have been so worn away as to be unrecognizable.
Some of them have orbits that cross the orbits of the planets and moons.
When they get close enough to a planet or moon, they will be pulled in by the large body's gravity and strike the surface at a speed of at least the escape velocity of the planet or moon, i.e., faster than a bullet.
The explosion is what carves out the crater so almost all craters are round (otherwise the great majority would be oblong in shape).