Can anyone shed light on lại? Where can it be positioned in a sentence? I'm confused.
"lại" comes after a verb, it means you do something again, do that one more time. In this sentence, "lại" is "again":
"read again" means "đọc lại",
"read that book again" = "Đọc lại quyển sách đó"
Additionally, it's also homophonous with a particle that denotes that one action happens rather than another.
e.g. Khi tôi đến thì anh ấy lại đi = He left when I arrived.*
Yeah I had a brain fart in that particular instance. It can be taken to mean either "When I arrived he left" or "He left when I arrived" or "He left as I arrived".
Also think of the prefix “re-” in English. To read something again is to reread something.