In order to send SMS there are two ways:
Sending SMS via Panel:
Enter the mobile number with the proper country code. Other than the mobile number, everything else i.e. Sender ID, content of the SMS etc. can be the same and you can send your SMS by filling these fields in the traditional manner.
Sending SMS via API:
You need to add a parameter "country=0" for international messaging and use numbers in their international format i.e. with country code.
For example- If you want to send SMS to any country, say UAE, you need to add "country=0" parameter in the API and the number on which you wish to send SMS should be mentioned along with the country code i.e. 971XXXXXXXX (971 being the country code for UAE)