Ok, kiddo, so there was a big fight in Spain a long time ago called the Spanish Civil War. Some people wanted the government to be a certain way and other people wanted it to be a different way. And when they couldn't agree on how to run things, they started fighting each other.
Now, lots of other countries were watching this fight from far away, like people looking at a TV show. And some of those countries decided they wanted to help one side or the other by sending soldiers or supplies. But there were also some countries that decided they didn't want to help anyone, and they wanted to stay out of the fight completely. That's what we mean by "non-intervention".
Those countries might have had different reasons for wanting to stay out of the fight. Maybe they didn't want to risk their own soldiers or resources, or maybe they didn't think it was their place to get involved in another country's problems.
In any case, non-intervention meant that certain countries refused to take sides or help either group in Spain. This might be hard to understand, but it's like if you were playing a game with your friends and some of your friends were fighting over the rules. Some of your other friends might want to just watch and not get involved in the fight, even if they have their own opinions about what the rules should be.
Does that make sense, kiddo?