Postal Mail Services
Mail (post) services are handled by the United States Postal Service (USPS). Unlike many other services in the U.S., the postal service is handled by the government. Many post offices may be very busy and have long lines. At some post offices, you just stand in the line for your turn. At other post offices, you take a number and you don't have to wait in the line. You can roam around, if you like. You go to the appropriate counter when your number is called.

ZIP Code
Postal code in the U.S. is called a ZIP code. A ZIP code consists of 5 digits, e.g., 90210 for Beverly Hills or 10001 in New York. There are also extended ZIP codes that are 9 digits (5 digits followed by a dash and then 4 digits). It may be faster in some places to use a 9-digit ZIP code, especially in big organizations. However, most people typically use a 5-digit ZIP code. It is very important to write ZIP code in every address. Every ZIP code in the U.S. has a post office.

Working Hours
Post office working hours vary. There may be some post offices open 24 hours a day in very big cities. However, most post offices are open from 9:00 A.M. to 5:00 P.M. There may be different hours on different days. The post office is open on Saturday until noon, if it is open at all.

Stamps
You can get stamps at the post office and other locations such as grocery stores, airports, etc. However, most people go to the post office to buy stamps. Most post offices also sell other supplies like tape, envelopes, greeting cards, and boxes. Many post offices also have a stamp vending machine so you don't have to stand in line. Some post offices may have a separate line just for buying stamps.

Occasionally throughout the year the post office will release seasonal stamps, such as for Christmas.

Mail
Mail is delivered on the days the post office is open, which excludes Sundays and federal holidays. If you live in an apartment, condominium, or town house, there may be several mailboxes side by side outside your home, and you will be given a key to get your mail. You will have to leave outgoing mail in the designated slot next to the mailboxes. For those who live in a house, there is a separate mail box for each house, mostly unlocked. You put outgoing mail in the same mailbox in which you receive mail.

There are blue mailboxes just outside the post office, and sometimes inside the post office. You put regular mail and priority mail in the bigger mail box. Express mail usually has a separate smaller mailbox. There will be instructions on the mailbox, such as mail pick up times, the maximum weight envelope/parcel that can go into the mail box, etc.

Mail Types
There are many different types of mail.

First Class Mail: A regular domestic airmail up to 13 ounces in weight.

Standard Mail: Generally used by big companies that do marketing by mail.

Parcel: Self explanatory.

Priority Mail: Speed post that reaches most places within the U.S. in 2 to 3 working days. Priority mail has flat rate envelopes available, and you can stuff as much as possible in that envelope without worrying about the weight. There is also a Global Priority Mail for international mail. The delivery timings vary depending upon the country and region of destination.

Express Mail: Express mail is like next day courier in most places. There is also a Global Express Mail for international deliveries.

Certified Mail: If you would like to be able to track the delivery of the mail, you can send it by certified mail. You will be given a tracking number that you can track online or calling USPS. It is a bright green color form. If you are sending certified mail, the same thing is called Registered Mail and it is a pink color form.

Return Receipt: If you would like the recipient to sign that they received your mail, you can send it by certified mail with return receipt. It is a dull green color form.

General Delivery
If you don't have a mailing address because you're temporarily staying somewhere, you can ask the sender to use the address c/o General Delivery.

John Smith
c/o General Delivery
Plano, TX  75093

Of course, you will have to go to the post office in person to pick up the mail, and you will have to show your photo identification to receive it.

Postage Rates
In May 2007, the USPS changed the postal rates drastically. It is no longer based on the type of mail you are sending and the weight of the mail. They keep all sorts of parameters in mind, such as from and to zip code, height, weight, length, thickness and various other things.

Therefore, other than most basic mail services, it is generally very difficult to find out accurate rates, e.g., 41 cents for up to 1 oz. first class mail within the U.S., 90 cents for mail up to 1 oz. to India and so on.

The best thing to do is to visit the USPS web site and calculate the postage.