How to dial internationally

On your phone, dial the country code then dial the city/area code (if any) for the number you're calling, and then the phone number you are calling.

Example: To call the United Kingdom, 44-123-4567891 (country code-area code-phone number)

Please note, in some cases the country code is shared among countries, e.g. the United States and Canada use country code 1. 

For reference, here is the complete International Country Codes list from CountryCode.org.