The plural is very simple in English. We usually use s to make the plural. We use s with 99% of words. Sometimes we use another form of the plural.
With some words, we change y to ies.
With some words, we use another word.
With some words, we use the same word.
The next day, we see a big storm. The waves are big. The waves are like mountains. The sea plays with the ships. The men are scared.
You can see more examples in the book Robinson Crusoe.