Sleeve Question - Pinwheel Sweater

Hi all,
I’m relatively new to knitting and am attempting my first big project, a pinwheel sweater!
Pattern Here: http://secure.elann.com/ShowFreePattern.asp?Id=138024

Now, I’ve made it to where I have 30 stitches between increases, which brings me to the “next round” portion of the pattern:

Next Round: knit the first set of 30 stitches and the yo from the round before, place the second set of 30 stitches on a holder, join a new ball of yarn and cast on 30 stitches using a provisional cast on - see below for provisional cast on instructions (this will be the sleeve later), join yarn and continue knitting 4 more sets of 30 stitches plus the yo’s from the previous round, slip the next 30 stitches on a holder, join yarn and cast on 30 stitches using a provisional cast on, knit the last 30 stitches and yo from the previous round.
Continue in pattern increasing and changing colour every 18th round until you have 42 stitches in each section.

I’ve got the second set of 30 stiches on a holder, but now I’m confused about “join a new ball of yarn and cast on 30 stitches using a provisional cast on”. Where do I join the new ball of yarn? What am I casting on to? Also, I don’t know what a provisional cast on is, but I see there’s a video in the cast on section of this site, so I’m sure I’ll be able to figure it out.
Then, after I cast on, it says “join yarn and continue knitting 4 more sets of 30 stitches plus the yo’s from the previous round”.
Just still confused about what yarn I’m joining in.

Maybe this would all make sense if I just started knitting some more, but I really don’t want to mess up my hours and hours of hard work I’ve done already.

Hopefully this isn’t too stupid of a question.
Thanks so much in advance for helping!
Sierra

I changed the title of your post because I know several people have made this and will be able to help.