Reading a pattern

Hello everyone, I am trying to teach myself how to crochet. I just do not understand some of the directions, so if you could possibly help I would be so grateful. I am trying to crochet an afghan and I will give you the first 3 Rnd's. It is the 3rd. Rnd that I can not figure out. Square Ch 4 join with a sl st in first ch to form a ring.

Rnd 1: Ch 1,, 8 sc in ring, join with a sl st to first sc.

Rnd 2: Ch 1 sc in first sc, [ch 4, sc in in next sc] 7 times, ch 1,dc in first sc to join and form last sp.

Rnd 3: Ch 1 (sc,ch 3 sc) all over dc, ch 2 [sc, ch 3, sc) all in the next space, ch 2] 7 times join to first sc.

Rnd 3 is a total mystery to me I don't understand the symbols or the brackets the way this is done.
I especially do not get the wording ALL OVER DC. ??? I appreciate any help you can give me.

Thank you so much.