Can someone tell me how many stamps?

Well, it depends on the weight of the envelope. If you go to this website http://postcalc.usps.gov/ then you can enter all of the relevant information, and it will tell you how much it costs. Then you have to find stamps which add up to the appropriate amount of money.

Within the US, you should only need one stamp per regular-sized envelope (assuming what you’re mailing isn’t heavy). Otherwise, just take your envelopes to a post office and they’ll calculate the postage for you there.

The distance doesn’t matter. As long as you are mailing inside the US, all the letters will take the same amount of postage. You will need one first class stamp for each one. If you need to send certified letters, you will need to take those to the post office and let them calculate the extra postage. If the evelopes are oversized or and odd size, like for a card, those will take extra postage. Extra weight will take extra postage. But distance for a letter is immaterial.

Just like coins, stamps come in many denominations. I have a whole roll of one-cent stamps. So it would take 44 of those. But I prefer to use a single 44-cent stamp for first-class postage. That will take my letter anywhere in the U.S., regardless of zip code, as long as it is in a standard envelope and weighs one ounce or less.

Use a “forever” stamp for ordinary letters. No need to worry about the exact amount of postage then.