In coding we have secure some information while we are sending it to server and vice versa ,In this case we use encoding and decoding . You can encode your information by using any method of encoding and when you will receive information from server then you have to decode that information using same criteria which is used by server side code to encode that information. For example
If you want to convert String to NSData using NSUTF8StringEncoding :-
var stri:String = "this is my string to convert to NSData"
let utf8str = stri.dataUsingEncoding(NSUTF8StringEncoding)
In above code, we have encoded stri to DATA using UTF8 encoding. When you have some data which is encoded in UTF8 Data than you can use below code