I'm writing a sci-fi novel, and I can't figure out how to start the book, as in how to introduce everything.

I have this book I'm writing, and everythong is planned out, but how do I strat it, I can write the middle parts and ending just fine, but Iv'e been wondering for over a year how to introduce it, showing the reader the information they need for the book without boring them, HELP PLEASE!