Okay, so you know when you want something and you say "Give it to me!"? Well, the antessive case is like that, but instead of saying "to me," you say "in front of me."
So, imagine you have a toy and you want your friend to give it to you. You point to the ground in front of you and say, "Give it to me on the ground in front of me!" That's using the antessive case.
It's like you're telling the person to put the thing you want right in front of you, so you can easily grab it. In some languages, like Finnish, for example, they use the antessive case to show where something is located in relation to someone or something else.
Basically, it's a way of showing the position or location of something in front of you. So, next time you want something, try using the antessive case and point to where you want it to be!