Ring structure is defined as the structure in which one or more series of compounds are joined or linked to form a ring. Ring can exist in different sizes such as cyclopropane (small ring: three carbon atoms) and cyclohexane (large ring: six carbon atoms).
In ring structure, there is only carbon atoms linked with hydrogen atoms which are identified by the linkage of two lines.
See the attached figure: cyclopropane (unlabelled atoms are carbon atoms with hydogens).
Thus, in ring structure, an unlabelled atom at an angle where two lines joined assumed to be carbon atom.