“Motivation in Fasting” (Matthew 6:16-18)

What does it mean to 'fast'? Is it something we are commanded by God to do? If so, how do we do it? For some it's a diet trend that keeps their body and skin healthy. Yet from God's intended meaning, it has spiritual implications that go way beyond the outer layer. Fasting is something that should and can be done in a proper way that honors God.