Jeans Or Jean

When we learn English, one of the most important things to know is how to talk about singular (one thing) and plural (more than one thing). You might  know that when there is one item (for example, 'book') we just 'a book' or 'one book.' When we want to say more than one book, we add the letter 's' after the word to become 'books.' 

In most cases, to make a singular noun to a plural noun, we add an 's' or 'es' after the word. 

However, as you can tell from the word 'jeans' there are some words that never have a singular form. Which means that even if there is just one item, we always use the plural form (jeans). If the word jeans is always plural, it also means that the noun takes on a plural verb ('are' not 'is'). 

As I've mentioned many times before, English can definitely get confusing  and it is near impossible to memorize everything. The best way to learn is to listen and speak more! It will start to become more natural for you!