This is one way to talk about the future:
I'm visiting Grandma Kate at the nursing home on Saturday.
I'm making supper for everyone tonight.
I'm not leaving, and that's that.
This form expresses a future plan that you're pretty sure about, and that has already been planned for. "I'm going to (do something)" expresses a plan that you're just a little less sure of:
I think I'm going to buy him a new camera for his birthday.
I'm not going to go to the wedding.