'prop' (noun)

When I look up the word ‘prop’, here is one of its meanings: ‘a small object such as a book, weapon etc, used by actors in a play or film’. However, I still can’t get it very well. Could you please explain more about these ‘small objects’?

Many thanks,

By the way, please also have a look at another meaning of its:

something or someone that helps you to feel strong
She was becoming an emotional prop for him.
=> I just wonder if we can replace ‘for’ with ‘to’…

Many thanks,

Everything on the stage that the actor handles is a prop. When the actor picks up the phone, it’s a prop. When the murderer fires the gun, the gun is a prop. When the hero picks up the handkerchief dropped by the leading lady, the handkerchief is a prop.

If there is a bowl of flowers on the back of the piano, but the actors never touch them, they are part of the set dressing.