Okay, so you know how sometimes people say things but they don't really mean exactly what they're saying? Like if someone asks you "Do you want to go outside?" but they're really trying to tell you that it's time to come inside and get ready for bed. That's called the illocutionary force - it's the hidden meaning behind what someone says.
It's like a secret code that grown-ups use sometimes to communicate without saying exactly what they mean. Illocutionary force helps to add more meaning and nuance to language. So if someone says "Could you pass me the salt?" with a calm tone of voice, that's just a simple question. But if they say it with an annoyed tone, it could mean that they are frustrated with you for not passing them the salt already.
Illocutionary force is really important because it helps us understand what someone is really trying to say, even if they don't say it directly. And it helps us communicate in more complex ways than just saying basic things. So next time someone says something to you, try to think about what they might really be trying to say with their tone and context clues!