Example 1
Susan and Sarah will open their Christmas presents at 4:30 in the morning whether their parents like it or not.
There's no such thing as "too early" when it comes to ripping the wrapping paper off a brand-new Barbie Dream House. In this sentence, the main verb, open, plus the helping verb, will, create the verb phrase will open, which is the simple predicate.
Example 2
Ann had never camped before.
In this example, the main verb, camped, plus the helping verb, had, join forces to create the verb phrase had camped, which is the simple predicate.
Example 3
Dinosaurs roamed the Earth for 165 million years.
That's a mighty long time. We puny little humans have only been around for about two million years. In this example, roamed is the main verb, and there are no helping verbs, so roamed is the simple predicate.