Confused by a pattern

[Swolff]

I am making a granny square blanket. I have sewn the middle large square together (six individual granny squares) now it looks like I need to do a border around the sewn squares. This is the directions: Join terracotta in any corner, ch 3, (2 dc, ch 3–corner made, 3 dc) in same sp, *ch 1, [3 dc in next ch-1 sp, ch 1] across to corner sp** at join of squares,(which I did) then it states: dc in next ch sp, dc dec in same ch sp and next ch sp, dc in same ch sp as last leg of dc decrease; rep from * across to next ch 3 corner, ending last rep at ** I’m so confused. 

[Granny Square]

The ** is a 'place marker'.  It occurs inside of a repeat.  You ignore it entirely until it tells you to deal with it. The reason is usually because the last part of the last repeat of the row or round needs to be different for some reason, and it will tell you what to do at that point.

Your pattern repeat says, in it's entirety (omitting your comment):

Spelling out 4 iterations of the repeat, you would do:

ch 1, [3 dc in next ch-1 sp, ch 1] across to corner sp** at join of squares, dc in next ch sp, dc dec in same ch sp and next ch sp, dc in same ch sp as last leg of dc decrease; rep from * across to next ch 3 corner

ch 1, [3 dc in next ch-1 sp, ch 1] across to corner sp** at join of squares, dc in next ch sp, dc dec in same ch sp and next ch sp, dc in same ch sp as last leg of dc decrease; rep from * across to next ch 3 corner

ch 1, [3 dc in next ch-1 sp, ch 1] across to corner sp** at join of squares, dc in next ch sp, dc dec in same ch sp and next ch sp, dc in same ch sp as last leg of dc decrease; rep from * across to next ch 3 corner

ch 1, [3 dc in next ch-1 sp, ch 1] across to corner sp** at join of squares

It should then say what to do after the  ** in the last repeat.

[Granny Square]

Meant to add this link, it tells you what all the crochet punctuation means https://www.craftyarncouncil.com/standards/how-to-read-crochet-pattern   Scroll down to 'parentheses , asterisks, and brackets' section.

There's other great stuff there, see the menu on the right side.