Newman projections of the chair:
The chair is much more stable as compared to the boat because the latter has eclipsed C-C and C-H bonds. This can be observed better in the Newman projections that have been drawn like that we are looking along two bonds at similar time - bonds 2-3 and 6-5. In the chair conformation, there are no eclipsed C-C bonds.
Figure: Newman projections of the chair and boat conformations of cyclohexane.
Figure: Ring ?ipping of cyclohexane.