Именно means "exactly". We use it either as a pair with "вот", like "вот именно", which is an exclamation meaning "Exactly!, Correct!, On the nose!", or separately, which conveys the same meaning but with less expression.
We also may use it as a means to put the sentence stress on a specific word, like a grammatical equivalent of this thing:
"Именно из-за тебя наша команда проиграла" = "It was because of you that our team lost" or
"Именно ты украл мою ручку, я уверен в этом!" = "It was you who stole my pen, I'm sure about that!"