Hello there and welcome!
Seed stitch is not difficult. All you need to do is knit a stitch, purl a stitch, knit a stitch, purl a stitch…(etc.)
In the following rows, you will continue doing this, and you will be knitting all the purl stitches and purling all the knit stitches. This will produce that bumpy texture (as opposed to the smooth texture of stockinette). NOTE: Be sure to bring the yarn to the front (between the two needles) before you purl a stitch, and back again before you knit a stitch.
That sentence about “Repeating last row twice” means just that. Do two more rows of seed stitch.
Have you checked out the videos on this site? They are very helpful. Don’t get discouraged. You will get it in no time!