The voice of a verb refers to the form of the verb used in relation to what the subject is doing. In English there are only two voices-- passive and active.
The active voice of a verb simply means the form of the verb used when the subject is the doer of the action.
In most writing, use the active voice. It is more direct and less ambiguous.
Passive Voice: The project was reviewed by the committee.
Active Voice: The committee reviewed the project.