Ceske Posta is the Czech post service. They provide the usual services of mail delivery, bill payment, etc. To calculate the postage for a letter or package, they offer a postage calculator.

To buy stamps, you can go to post offices, shops, and news stands (tabaks). To mail, just put your mail in one of the bright orange post boxes located around the city.

How to Address envelopes:
First name, LAST NAME,
POSTE RESTANTE, post office address,
Postal code, city, CZECH REPUBLIC

Main Post Office
To receive service, take a numbered ticket from near the door. There will be a lit board to let you know when it's your turn. There are different counters for different services:
Listovni sluzby - buy stamps there and send items recorded delivery
Balikove sluzby - send individual parcels. This is also where to bring the notification slip you get in your mailbox when you are the receiver of a package. Must have a passport or other ID to claim package. Note: you may be asked to pay a fee to cover customs
Vyplata poukazek - counter to pay bills

Address: Praha 1, Jindrisska 14 (near Wenceslas Square)
Tel: 257 32 27 92
Hours: 08:00 - 18:00. Closed Sat, Sun

If you are looking for another office, go to the Ceska Posta's office locator.

Recorded Delivery (or Registered Post) needs to completed at the post office. A postal receipt (podaci listek) will be filled out and attached to the piece of mail. Once the mail as been delivered by hand, the receipt will be signed and returned to the sender as proof of delivery. This service is an additional charge.

To send airmail, specify letecky (by plane). For international packages over 2 kg, you will need to go to the customs office.

Companies

DHL
Address: Praha 6, Aviaticka 1048/12 Telephone: 420 800 103 000
Hours: 08:00-18:45, closed weekends

Fedex
Address: Praha 4, Olbrachtova 1 Hours: 08:00-19:30, Sat 08:00-13:00, Sun Closed.

UPS
Address: Praha 6, K letisti 57/1049
Telephone: 420 800-181-111
Hours: 07:00-18:30, closed weekends