Okay, so imagine you and your friend both really like playing with toy cars. But you both have different favorite colors of cars - you like red cars and your friend likes blue cars. Sometimes when you play together, you might disagree about which color is better or which car is faster. You might even get a little competitive with each other because you want your cars to win.
That's kind of like how Spanish football rivalries work! There are lots of different teams in Spain that play football (which is like soccer, but in Spain they call it football). Some of these teams are from different cities or regions, and they often become rivals because the people who live there have different preferences and opinions about which team is the best.
For example, two of the biggest football teams in Spain are Real Madrid and Barcelona. Real Madrid is based in the city of Madrid, and Barcelona is based in the city of Barcelona. Even though they are far away from each other and have different fan bases, they still play each other a lot and have a big rivalry. The fans of each team might argue about which team has better players or which one deserves to win the most.
There are lots of other rivalries like this in Spanish football, too. Some are based on regional or historical differences, like the animosity between Athletic Bilbao and Real Sociedad, two teams from the Basque Country, or the rivalry between Valencia and Villarreal, two teams from the eastern coast of Spain. And sometimes rivalries can get really intense - fans might even get into fights or do things to try to mess up the other team's chances of winning.
Overall, Spanish football rivalries are kind of like friendly arguments between friends who support different toy car colors - except instead of toys, it's football teams, and instead of just playing around, they're playing a serious game with lots of fans and lots of emotions involved!