Where could I send the coin in to grade it?

I have heard alot from ppl in here. so could someone teach me how to do it. which places I can send in, and how to send it.
and why you have to send the coin in to grade it? is there more value when it graded then normally in hard plastic cover?
and why you have to send the coin in to grade it? is there more value when it graded then normally in hard plastic cover?
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