Hi there,
Mood means to create setting and attitude. Authors use moods to describe a certain character like in a story they'll describe a person's mood towards something or someone. The mood creates tone which the audience or readers look for in the story. That usually what makes a story interesting.
Theme means the central topic that a text creates. It creates a big message or a big idea like when an author writes a poem they use certain themes to create the perfect tone in the story that has multiple meanings in that poem.
The authors use these types of tools to create a story that will make the audience like it and make them fascinated.
Hope this helped :)
Have a great day