Superglobals for form info and with header()

I am a newbie and was confused for a while by Superglobals because I had to amend all the examples in my books. (Lots of beginners stuff is about taking in information from forms straight into variables with the same name as the form input). I think the answer is essentially to relace the example variables with $_POST["VariableName"] or $_GET["VariableName"] instead of using directly $VariableName. Or perhaps to read the value from the array into some other new variable. This did cause me a problem when bringing in a number - the answer seemed to be to define the new variable as an integer. $NewVariable=(int)S_POST["VariableName"] seems to be right. But I am not sure I understand why it is more secure. Two questions - 1. Is this more or less right and what else do I need to do to work the new system in all my examples? (I want to learn the 4.2 way from the beginning). 2. Does the new Superglobal arrays way of doing things apply if I transfer information over using header()?