들 is the plural suffix in Korean language.
You can use 들 after a noun like 개들, 고양이들
But, 들 is rarely used with nouns denoting inanimate objects. It is more often used with nouns denoting animate objects (people and animals), but then only when it is semantically necessary to make a distinction between singular and plural, or to emphasize plurality.
two dogs would be "두 마리의 개" or "개 두 마리" . 두 마리의 개들 is awkward
two people would be "두 사람" . 두 사람들 is awkward