The telephone code of Thailand is 66. To call to Tai from Russia, you first need to dial "8", wait for a dial tone, then dial "10" for the international call, and after that the code of Thailand is 66. Then you will need the city code and phone number itself. For example, in Bangkok code 2, so to call there, you will need to dial:

8-ring-10-66-2-phone number.

Telephone codes of other cities in Thailand, see here.