Here's an example I saw:
誰かがおいしいクッキーを全部食べた
Translation: Someone ate all the delicious cookies
Literal translation: Someone (subject marker) delicious cookies (direct object marker) all ate.
It's not technically listed in the definition but you can also take 全部 as meaning "everything". You wouldn't say "Everything is in this together", but rather "Everyone is in this together", so you wouldn't want to use 全部 to translate this sentence.
"Everyone" in Japanese is 皆「みんな」or 皆さん「みなさん」, the latter being more polite. That said, "We are all in this together" is an idiomatic sentence, so its translation would look pretty different in Japanese. You might simply say 「皆で頑張ろう」, which just means "Let's all do our best."
全部、isn't usually used to talk about people. it's used pretty exclusively just for things.
to answer your question, 全部is often used like,
全部食べて下さいplease eat all of it.
ええええー美味しそう全部食べたい。omg, i wanna eat all of it.
let me know if this helps. :)
In what instances would this word be used
For example of I am trying to say ''We are all in this together" would I use this kanji/reading or would I use a different kanji/reading?