It depends on what part of them is broken, you really need to specify more information. That being said, I'll put forth a few scenarios.
If a wire is broken, you can splice it back together. However, soldering the connections together would be a far better option. Broken wires are probably the easiest to repair.
If the ear piece broke off, you could try gluing it back to the main part of the earphone, however it might not bond well enough to be sturdy.
If the earphones are relatively inexpensive, you could simply buy another pair and avoid the headache.
