Row 3 is decreasing by 1 stitch on each end. A sc2tog is "single crochet 2 together," and it decreases by 1 stitch each time it's performed. There should be 63 sts at the end of this row.
Row 4 and 5 are poorly written. At least (I hope) you have a picture of what you're going for...when you've posted maybe one more message, you'll be able to post an url of the pattern, if there is an url.
The idea of Rows 4 and 5 (and maybe 6 through 13; that's the "poorly written" part) is that you keep crocheting the set-up established in Rows 1, 2, and 3. Row 3 decreases by 2 sts, at the beginning and the end, so to decrease from 65 to 55 sts means 5 repetitions of the 3-row cycle, or 15 more. However, that's 15 rows, not 13.
If you repeat Rows 2 and 3 only, you'll still decrease those 2 sts, but will need only 10 additional rows.
If the pattern designer has a website, check to see whether there are any "errata" or take a good look at the picture/photo to see whether it appears to have a total of 3+15 = 18 rows or 3+10 = 13 rows.
"Fasten off" is how you end a piece of crochet. Cut the yarn about 6 inches beyond the last stitch. Pull the tail back through the last stitch, forming a small knot. Weave the end back through the sts with a yarn needle. Done!
Learning crochet and knitting at the same time....that's a lot of work!