What does this command line error mean?

Question

git

I changed the code in the file. When I try to push changes to github, I get the following error

. Why is it? And how to solve it?

The question was solved, the answer is here: What is the error when pushing in Git?

Answer 1

Everything is written there. Someone has already made changes. You need to pick them up and do a git pull and only then push your own.