你 (nǐ) means you (singular), as explained previously.
很 (hěn) means very, quite, highly.
老實 (lǎoshí) means honest, frank, straightforward, well-behaved, kind. It is honest and kind and, in a sense, honest and nice to a fault.
Example: A co-worker of mine always does the right thing. To him I would say, 你很老實 (Nǐ hěn lǎoshí).