Learn French: Il est petit, mais ils sont grands. - He is small, but they are tall.

In this sentence, they sound exactly the same! The s at the end of ils is silent. You can only tell it is plural because the verb changes from est to sont.

Why does the verb change from est to sont?

Both are forms of the verb être (to be). Est is the singular form used with il (he is), while sont is the plural form used with ils (they are). This is just like changing 'is' to 'are' in English!

Why does grands have an 's' at the end, but petit doesn't?

In French, adjectives have to match the subject they describe. Because ils (they) is plural, we add an s to the end of grand to make it plural too. Since il (he) is singular, petit stays in its singular form.

Do I pronounce the 's' at the end of grands?

No, the s at the end of grands is silent. In fact, both the d and the s are silent here, so it sounds just like the singular word grand. Similarly, the t at the end of petit is also silent.