the 3 hydrozen atoms are in a plane and attached to one a C in the plane perpendicular to C - C bond. In eclipsed form, Look along the axis or C - C bond and perpendicular to plane of hydrozen atoms. Then you find that 3 hydrozen atoms attached to the rear C are exactly behind the front 3. C is behind C.
In staggered conformation, The H atoms in the front are rotated by some value. So if you look along C - C bond, 3 front H atoms and 3 rear H atoms are all visible.