Needle size depends on the yarn you are using and the gauge you get with that yarn. You can make socks from lightweight (fingering) yarn on #1 needles, midweight (DK) yarn on #4 needles, or worsted weight yarn on #8 needles. Or different needle sizes altogether, depending on how loosely or tightly you knit.
No matter how new a knitter you are, you've got to get your head around the idea of gauge. Patterns alone don't guarantee that you'll get the size you want. Gauge is simply a matter of how many stitches per inch you get with a given yarn and needles. Yours may be entirely different from the designer's.
Charlene Schurch's books are excellent for helping you figure out what needle size to use with a specific yarn. Another good one is Ann Budd's book, Getting Started Knitting Socks. (But with any of them, you'll still have to know your own personal, individual gauge.)