The ground state conformation of cyclohexane is a fully staggered conformation which is shaped somewhat like a "chair". To strike a balance between torsion strain and angle strain and to achieve more stability cyclohexane attains various conformations out of which chair and boat  form are most significant. In chair conformation, the C-C-C bond angle can reach the strain free tetrahedral value(109.5) and all neighbouring C-H bonds are staggered. Therefore this conformation does not have any torsion strain or angle strain.In this conformation, there are two types of position for substituents on the ring, axial(perpendicular to the ring or parallel to the ring axis and equatorial(in the plane of the ring). Therefore six hydrogen atoms are in axial position known as axial-hydrogen and six hydrogen atoms are in equatorial position known as equatorial hydrogens