Practically anything can become ionised by either losing or gaining electrons from the outer orbits or shells. The ionising process can be accomplished in many ways. For example spraying a liquid through a very fine jet can cause electrons to be lost, creating positive ions (electrons are negative in charge and so their loss results in a net positive charge).
Other wise, substances can be bombarded with high energy particles causing electrons to be lost again.

Basically the process of ionisation, is the process of creating ions - of either charge. The take home message being that the process results in the substance now having a net electrical charge.