How to display specific text for a single category?

To appear in the category and displayed on the pages is as follows:

if (
 $_GET['cat']=='25' and
 (empty($_GET['page']) or $_GET['page']=='1')
){
 echo 'text';
}

Stands like this:
"if the category is equal to 25 and the page is blank or equal to one then print the text."

It's pretty easy code, you'd probably want to learn php, then you will be able to make this logic.