+7 then city code then local number. the city code for Moscow is 495 (instead of 095) for many years already.

for a moscow seven digit number like 123-4567 you would dial +7 495 123-4567.

Many mobile numbers use a city code like 916 or 903 or 915 or 985 or 499 etc. These are special city codes mostly reserved for mobile phones. They are often written with an 8 at the front, which is what you would dial inside russia to reach a different city code. So if somebody had a mobile number 123-4567 with city code 915, it will often be written as 8-915-123-4567. To call that number from outside russia you would strip off the 8 and replace it with +7 and the result is +7 915 123-4567. (In this case 8 is very similar to the leading 0 used in many UK numbers for inter-city calls.)