Plurals aren’t really a part of Japanese. In fact, many Japanese people that I have met just can’t seem to grasp the concept of why we need to add an “s” to so many words in English. Of course, I can’t imagine communicating without it (Although I do) !
There is one exception. When indicating a group of people, the suffix 達 (taw chee) can be used. The most common way to use it is for “we.” 私 (waw taw shee), which means “I”, can be changed to “we” by adding 達. Example: 私達 or 私たち. The (taw chee) is often written in hiragana.
In the same way, “they” (both male and female) can be made.
彼達 (kaw ray taw chee) This means: “They” for males only or for mixed groups.
彼女達 (kaw no joe taw chee) This means: “They” for a group of females only.
達 is never used for non living things.
ら is another suffix for making plurals. It is more casual and can’t be used the same way as 達.
ら can be used to refer to people of equal or lower status, but not higher.
Another interesting point is that it cannot be used to refer to a group that includes yourself. So 私ら is NOT correct. In that case,達 is the only one that can be used.
But again, my advice is to go with the more polite way. You can never go wrong.