How to create a leaderboard on Android and iOS ?

Hello guys,

I'm well aware there were a few people asking about this question before. However, I was only used to creating offline scripts (which don't involve online processes), so I'm pretty much at lost right now, trying to understand what people are talking about. So, can anyone give me a guideline to how I can create a worldwide leaderboard on Android and iOS ? The more detailed it is, the easier it will help a dumb person like me to understand. Thank you very much !