Don't bother with the grammar books. Here's the simplest definition of the active voice we've seen.

Definition of active voice

Active = Actor/s + Verb - in that order

Examples of active voice:

Vanessa (actor) arrived (verb) at 9am.
We (actors) met(verb) her at reception.

The actor or actors might not be human. If they are acting, they are actors.

The path (actor) led (verb) to the best view of the mountain.
Appendix one (actor) lists (verb) all the data.