You'll see this attached to other words to make them plural. That's why it's called a pluralizing suffix (or a plural suffix for short).

〜達 is stuck onto the end of nouns (usually people or animals) to make them plural. It can also be used with a person's name, like マリア達. In that case, it refers to Maria and the group of people she's with (rather than a bunch of Maria clones or something).

Note that you'll often just see this word written in hiragana as 〜たち.

This is almost the same reading you learned with the kanji. Remember たつ? Well this is read たち. Here's a mnemonic to help you remember it:

If you want to pluralize something, touch (たち) it to something else. One friend touches another friend, well now they're friends. Plural friends! All thanks to the good ol' pluralizing suffix touch!

Oh, and don't type the 〜 out when writing the answer. It's just there to let you know that there's usually something attached in front of this word.