Let Go and Let God

What does it mean when we say "Let go and let God?" If you've never heard of this let me explain it. This is something we as believers say when we are going through trials of life. We must place the problem into the hands of God, by faith. Praying asking him to help us and trusting that he will. It's by faith.  

1 Peter 5:7 Casting all your care upon him; for he careth for you.