Similes always include the word “like” or “as” to compare two things. We use similes to compare things that are quite different but that have a quality that is similar. Eg. Nomsa was as fierce as a lioness.
A lioness is very different from Nomsa but they have a quality that is the same: they are both protective of their young and are quick to attack anyone who threatens their cubs or children. Comparing Nomsa to a lioness gives us a good picture of just how frightening Nomsa can be.
People use similes to make their writing more interesting and descriptive.