00 isn't part of the country code, it is a commonly used international dialing prefix.
Country code +90 is Turkey, and area code +90 534 indicates a mobile phone served by Turkcell.
(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)
00 is a commonly used international access prefix, not part of the telephone number. +232 is the country code for Sierra Leone, in western Africa. +232 22 is the city code for Freetown, the capital of Sierra Leone.
The country code for Poland is +48, and Kraków is city code 12. From the UK, dial 00 48 12.
'00' is not part of the country code, it is a commonly used international access prefix. Country code +249 is Sudan, and +249 92 is a mobile.
'00' is not part of the country code, it is a commonly used international access prefix. Country code +212 is Morocco, and +212 6 is a mobile.
Country code +358 is Finland.
Dialing from the USA, 00 44 would be UK. 00 is the international access code in USA followed by the country code of UK which is 44.
'00' is not part of the country code, it is a commonly used international access prefix. Country code +880 is Bangladesh, and +880 19 is a Banglalink mobile.
'00' is not part of the country code, it is a commonly used international access prefix. Country code +27 is South Africa, and +27 78 is an MTN mobile.
'00' is not part of the country code, it is a commonly used international access prefix. Country code +62 is Indonesia, and +62 819 is an XL Postpaid mobile.
'00' is not part of the country code, it is a commonly used international access prefix. Country code +269 is the Comoros Islands in the Indian Ocean.
'00' is not part of the country code, it is a commonly used international access prefix. Country code +682 is the Cook Islands, but there are no valid numbers beginning +682 0.
'00' isn't part of the country code, it is a commonly used international access prefix. Country code +90 is Turkey, but area codes in Turkey are three digits, so you need two more digits to determine the city.