1.
Knit one stitch and then purl one stitch. Repeat this until you reach the end of the row.
2.
Seed stitch alternates purls and knits in both columns and rows, so for every row you should be looking at the stitches of your previous row to decide whether to knit or purl. You'll need to purl every knit stitch and knit every purl stitch, as you should never have two knits or purls together.
Tip: If a stitch appears to have a horizontal strand of yarn across the bottom of it, this will be a purl stitch and if it doesn't have this horizontal strand it will be a knit stitch.