Purling is quite easy. It's pretty much just like knitting, but exactly the opposite. Knitting is in the back of the stitch, purling is in the front. If you purl every row, you'll end up with garter stitch just like if you knit every row.
When you're done the whole row of purl it will look like this.
If you just keep going with a the purl stitch on the following rows, you'll be knitting the garter stitch. If you want to try something new ...
Stockinette is a great stitch for when you want a block of flat knitting, like a sweater or hat. For things like scarves it isn't so great because the edges tend to curl. You can put a border on the knitting to help ease the curl if it's what you want. I think it looks good with a border of garter or moss stitches.
The pattern is really easy to follow:
Row 1 (right side): Knit
Row 2 (wrong side): Purl
Repeat those two rows for as long as you like. It will look like this:
This is a pretty common stitch as well. It's used often for the cuffs of mittens or the first couple inches for socks. It does eat up more yarn than stockinette or garter stitch, so plan for that if you want to use this stitch. I think it tends to shrink the width of the knitting in half. For instance if the number of stitches you have gets 4" in stockinette stitch, it might only be 2 or 2.5" in ribbed stitch. It's always best to knit a swatch, or 4" by 4" square, first to make sure you have the right number or stitches and the right size needles.
This is the first row:
The second row:
Here is the pattern if that's easier to follow.
Ribbed stitch with an even number of stitches:
Row 1 (RS): k1, p1, repeat to end
Row 2 (WS): repeat row 1
Ribbed stitch odd number of stitches:
RS : k1, p1 repeat to end
WS : p1, k1 repeat to end
It will look like this:
You can see just how much narrower it makes the knitting even though it's the same number of stitches. There are a couple of things that can affect the rib stitch. If you use a needle that is larger than what is required for the tension, your ribbing will be less elastic. Also, the higher number of stitches in the rib the less elastic it will be. For example a K4, P4 rib will be less elastic than a K1, P1 rib.
Whew! That's a lot of knitting.
Take a break. Go outside. Get some fresh air. Your knitting will be waiting for you when you get back!