To expand on what the others said, yes it is for plural but you should remember that it does not work for all words, mostly only for human pronouns. あなたたち would just be "you (plural)", which is not something we have in English, but exists in a lot of other languages.

hello，i am glad to answer you。 達like show 2 or more than 2things ……for example 私means me ，and 私達means we 。

You used it to say the plural. 私たち、we あなたたち、you (plural) たち　is the pluralizing suffix like for people, animals :)