Instead of being planar, cyclohexane twists into something called a chair conformation to reduce angle and torsional strain.
Concept #1: What is a chair conformation?
By twisting into a chair, angle strain and torsional strain are now effectively zero.
Concept #2: How chairs flip from one conformation to another
In order to flip from one chair to another, the cyclohexane must first pass through a boat conformation (not stable due to flagpole interactions of hydrogens!).
Concept #3: How chairs flip from one conformation to another