"Actúa solo según aquella máxima por la cual puedas al mismo tiempo querer que se convierta en una ley universal"

Simplified Meaning:

This quote is talking about a way to decide if something is the right thing to do. It suggests that before you do anything, you should think about whether it would be good if everyone else did the same thing. If it wouldn't be good for everyone to do it, then you shouldn't do it either. For example, imagine you are thinking about cutting in line at the grocery store. Before doing it, consider if it would be okay if everyone cut in line whenever they wanted. If everyone did that, the line would be a mess and no one would get their turn. Since that wouldn't be good, you shouldn't cut in line either. This advice can help people act in ways that are fair and respectful towards others. By thinking this way, you help create a better, more orderly, and just world. It's about treating others how you'd want to be treated and thinking about the bigger picture before making decisions.