An anticausative verb is a special type of verb that shows something happening without anyone making it happen. Imagine you are playing with your toys and suddenly one of them falls off the table. No one pushed it or touched it, it just fell by itself. That's what an anticausative verb shows - something happening all by itself.
Let's take another example. Imagine you are sitting in your room and suddenly you feel sleepy. You didn't eat any special food or take any medicine, you just suddenly started feeling sleepy all on your own. This is how an anticausative verb works - it shows something happening without any cause or external force.
In summary, an anticausative verb is like a magic trick happening in a sentence, where things happen by themselves without any magic wand or external force.