Copy Location Constraint
The Copy Location constraint forces its owner to have the same location as its target.
Note that if you use such a constraint on a connected bone, it will have no effect, as it is the parent's tip which controls the position of your owner bone's root.
These buttons control which axes are constrained.
Invert their respective corresponding axis coordinates.
When enabled, this control allows the owner to be moved (using its current transform properties), relative to its target's position.
Standard conversion between spaces. See common constraint properties for more information.
Controls the percentage of affect the constraint has on the object. See common constraint properties for more information.
Let us animate a solar system with the Copy Location constraint and its Offset option. You can make the owner, called "moon", describe perfect circles centered on the world origin (using e.g. Location X/Y sine and cosine F-curves, see Built-in Function Modifier). Then copy the location of a target "earth" with the Offset checkbox enabled to model a satellite in a (simplified) orbit around its planet. Repeat these steps for more planets circling around its center star "sun".
Following video is a small animation of a solar system created using (among a few others) the previously described technique:
Note that, this 'solar' system is not realistic at all (the wrong scale, the earth is rotating in the wrong direction around the sun, ...).
You can download the blend-file used to create this animation.
Furthermore you can also animate a few properties of each constraint using animation curves: e.g. you can animate the Influence of a constraint. It is used to first let the camera follow the moon, then the earth, and finally using two Copy Location constraints with Offset set.