1) The CSS code box should go somewhere between <head> and </head>
2) White should be #FFFFFF and Blue #0000FF (the first two numbers after the # refer to the amount of red in a color, the second two refer to the amount of green, and the last two refer to blue - they go in hex, which is 0 to 16 (0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F)
3) 'slink' is a name of called a class. Rather than type exactly the same information for every link on the page as to their colour and style, you can give them a name, so if you want to change it you can only change it once in the CSS
4) What you have to do is for every link you want white you put <a href="/pagelink.html">linktext</a> and for any blue link, put <a href="/pagelink.html" class="slink">linktext</a> (with "pagelink.html" and "linktext" being replaced with your page to link to and what you want your linked text to be respectively).