Active means the subject performs the action, the action is being performed.
Passive means the action is performed upon someone or something.
It's a difference between doing and happening.
Keepin' it Simple For Ya.
The main verb is "was" or "were" and is followed by an "-ing verb." To wit: "He was walking past the pond." Much better: "He walked by the pond..." See how that also opens up the sentence for more detail? "He walked by the pond, stale bread for the ducks in hand." Now, it's not only active, we know why he was walking by the pond.
Easier to Find Than You Think.
Google "vivid verb lists." Here's a sampling of what I found. Check 'em out!
High School Vivid Verb List
The Vivid Verbs List of All Time
A 1000 Verbs to Write By, by Deanna Carlyle
And that's your Editor's Desk Tip of the Day.