Scroll down to the Conclusion section on the page you linked and download the provided NSData+Base64 files. Its the best solution I have seen so far and is incredibly easy to use. If you can learn anything about Cocoa, you can learn to use that project.
Example
NSString *originalString = [NSString stringWithFormat:@"test"];
NSData *data = [NSData dataFromBase64String:originalString];
NSLog([data base64EncodedString]);
The above will print out the original string after converting it to base64 and back to a normal unencoded string.