The commands used in the small piece of code are very elementary. So you have to read the manual because all the answers are in there.

I cannot explain how an If-Then-EndIf statement is syntaxed or how is working. The code I gave you is very very easy and basic I could say.

It is comparing one element of the array gsmbuffer at a time with one element of the other array. If it succeeds then it is moving on to the part of the program labeled:

correct_sms:
'you add your code here

If it does not succeed then it is moving on to the part of the program labeled:

wrong_sms:
'you add your code here

Try to write some code and see what happens. One part at a time...

Ioannis