One funny true Hollywood story is about Marilyn Monroe. She was once filming a scene where she had to walk through a door, but she kept getting her high heel stuck in a crack on the floor. Instead of getting frustrated, she started laughing, and that laughter was so contagious that the whole crew joined in. It took them a while to fix the floor and get the shot right, but it became a memorable moment on set.
A really interesting funny story is about Charlie Chaplin. He entered a Charlie Chaplin look - alike contest in San Francisco and lost. He was so good at creating his own unique look that people didn't believe he was the real Chaplin. It was quite ironic and funny at the same time.
It's hard to say for sure. Some might be based on real events, but often there's an element of exaggeration or fictionalization for entertainment purposes.
It varies. Some Hollywood series are directly inspired by true events and try to stick closely to the facts. Others take elements from real life and build a fictional story around them. And then there are those that are purely made up for entertainment.