This document discusses properties of cyclic groups and subgroups of cyclic groups. It provides examples and proofs of theorems regarding cyclic groups. Specifically, it states that a subgroup of a cyclic group is cyclic, the order of any subgroup of a cyclic group must divide the order of the group, and for each positive integer k dividing the group order n, the group has exactly one subgroup of order k. It also provides examples of finding the order of elements in cyclic groups and calculating the Euler phi function for various numbers.