There exist many different conformations for cyclohexane, such as chair, boat, and twist-boat, but the chair conformation is the most commonly observed state for cyclohexanes because it requires the least amount of energy. The chair conformation minimizes both angle strain and torsional strain by having all carbon-carbon bonds at 110.9° and all hydrogens staggered from one another.
The molecular motions involved in a chair flip are detailed in the figure on the right:  The half-chair conformation (D, 10.8 kcal/mol, C symmetry) is the energy maximum when proceeding from the chair conformer (A, 0 kcal/mol reference, D symmetry) to the higher energy twist-boat conformer (B, 5.5 kcal/mol, D symmetry). The boat conformation (C, 6.9 kcal/mol, C symmetry) is a local energy maximum for the interconversion of the two mirror image twist-boat conformers, the second of which is converted to the other chair confirmation through another half-chair.  At the end of the process, all axial positions have become equatorial and vice versa.  The overall barrier of 10.8 kcal/mol corresponds to a rate constant of about 10 s at room temperature.  
Note that the twist-boat (D) conformer and the half-chair (C) transition state are in chiral point groups and are therefore chiral molecules.  In the figure, the two depictions of B and two depictions of D are pairs of enantiomers.
As a consequence of the chair flip, the axially-substituted and equatorially-substituted conformers of a molecule like chlorocyclohexane cannot be isolated at room temperature.   However, in some cases, the isolation of individual conformers of substituted cyclohexane derivatives has been achieved at low temperatures (–150 °C).