Modern Greek is a language that people in Greece speak today. It is different from Ancient Greek, which is a really old language that people spoke a long time ago. Modern Greek uses letters and sounds that are similar to English, but there are some differences. For example, there are some letters in the Greek alphabet that don't exist in English, like "ε" and "υ".
In Modern Greek, words are made up of different parts called syllables. These syllables are put together to make longer words. And just like in English, each word has its own meaning. If you want to say "hello" in Modern Greek, you would say "γεια σας" (pronounced "yia sas").
People in Greece use Modern Greek to communicate with each other, write books, newspapers, and even make jokes in this language. They learn it in school, so they can use it to talk to others in their country or to visitors from other places.
Some people might think that because they speak Greek they can understand other languages like Spanish or French, but that is not really true. Modern Greek is its own language, just like English or Spanish, and has its own unique characteristics.