Now that you've got the right needles and you've done your gauge swatch, it's time to start your sweater. Woo hoo!
Getting the yarn on the needles, you'll want to do a stretchy cast on to accommodate the ribbing that comes next. Long tail cast on is a great one for this as it gives some extra stretch.
A lot of patterns have some short row shaping to lower the neckline at the front. This is done at the back of the neck with wrap and turns. I know wrap and turns can be a little confusing, so check out this slow motion video from Very Pink Knits. (She has faster ones too if you prefer.)
The Grouse Creek sweater jumps right into colourwork. The best way to do colourwork is to hold a strand in each hand. It will help you have even tension, keep the yarn from tangling, and help you catch your floats. Here is a PDF that give some instructions for doing colourwork. If you'd like to watch some videos, Very Pink Knits has some good ones.
The colourwork for Grouse Creek is done from a chart. When reading a chart we start and the bottom and work up to the top, and we start on the right and work to the left. There are some blank spaces on the chart because of the increases as we work around in the yoke.
Remember you can stop by the store anytime if you need some help. It's not always easy learning by written instructions or YouTube videos.