The international phone code of Russia is "7", the code of Samara is "846".
If you call to Samara from abroad , you should dial the international access number (usually 00 or "+"), then the code of Russia "7", then Samara (846), and then the 7-digit city number.
If you call to Samara from any place in Russia , dial 8, wait for a tone, then dial the Samara code (846), and then the 7-digit city number.
If you dial a Samara number inside Samara , just dial the 7-digit number, without any prefixes. The calls inside the city are free, except in hotels (check how much they charge).
The best place to make calls is at the Main Post Office or at Volga Telekom. To make a phone call, first queue for the operator, pay an advance for a call and then they'll tell you what cabin to go to make a call. Once your call is finished, you can get back the money you paid, if you haven't used it all already.
But if you plan to stay in Samara for a longer period it is very cheap to buy a SIM card with any of the local operators: MTS, Beeline or Megafon are the main ones.. If you already have a Russian SIM card with one of the main networks it will also work in Samara, though you will be charged slightly higher “internal roaming” tariffs.