Answer:
I was flying.
I saw a plane flying.
A ball flew by me.
A bird flew over me.
I like to fly planes.
In all of the sentences above, "fly", "flying", "flew", etc, are all words that act as the action in the sentence.
Verb - The action of doing something. Example: Throwing, walking, running, etc. A good way to remember if a word is a verb is if it has "ing" at the end of it. (A verb doesn't HAVE to have "ing" after it, but if a word does, it's most likely a verb).