For a reader to contrast two or more things, the reader must consider how they are

alike
different
similar
comparable

To contrast two or more things, the reader must consider how they are different and similar. Comparability may also play a role in contrasting the items.

To contrast two or more things, the reader must consider how they are different. It is important to identify the contrasting features or characteristics that distinguish the topics from each other. By examining these differences, the reader can gain a deeper understanding of each individual topic and how they vary from one another.