The easiest way to "merge" two object would be to select your object first, and select the object you want it to merge into second, and press CTRL+J. This will join both objects into a single object, thus sharing verts.
If you want to keep the two objects separate however, but share properties, do the same as above, but instead of pressing CTRL+J, press CTRL+P to parent the first object to the second one. You can also choose parent under the object tab (The one with the orange cube).
If you want the two objects to stay completely separate, but share some information, like location, you can use constraints (It's the tab with the chain icon).
Hope this helps.