The basic playing position for acoustic guitar is with the guitar resting on your right thigh, balancing enough so that your left hand does not need to do the work of supporting the guitar’s weight. To begin learning how to strum your acoustic guitar, take the E minor chord in the first position and strum all six strings with the pick in a downwards direction. Your pick should be at right angles to the strings so that it strikes the notes without a dragging sound.
If you practice playing up and down strokes, randomly at first, to get the feel of strumming comfortably, you can move onto playing in 4/4 time and changing chords as you go. If you practice playing in time you will develop the trick of picking up the strumming pattern a guitarist is using on a recording. This is much less trouble than trying to learn strumming patterns from CDs without first getting some practice under your belt.
Here is a video from Guitar In A Nutshell which gives you details about how to strum . . .
There is also a nice video lesson on strumming for beginners at Acoustic Nook.