Copyright means that only you have rights to do certain things with your work. You have the right to:
reproduce or copy your work
communicate your work to the public, for example by broadcasting (TV, radio), by email or on the internet
publish your work
perform your work
adapt your work
Other people need your permission to do any of these things, even if they have bought or own the original work. This is because copyright ownership is different from ownership of the physical work you created.
For example, if you create an oil painting on canvas, the physical work is the canvas with the oil paint you used. You own it until you have sold it or given it to someone else. Once you have done that, you do not have ownership of the physical painting but you still own copyright in relation to the image you painted.