It is easy, and Flow has made several videos to help you. The exact answer depends on what you buy. I usually buy 5-frame nuclei. That means 5 frames of bees, brood, honey and pollen. You simply transfer the 5 frames into your Flow brood box (in the same order and orientation that they were in the nucleus box), add 3 empty frames, and put the cover and roof on top.
Packages perhaps require a little more thought, but the Flow video was made by @Michael_Bush, and I couldn't possibly explain it any better than he does. You can search for it on YouTube. Takes about 30 minutes the first time you do the installation, and less than 10 minutes when you have done it a few times.
In your region, you probably need a second brood box, so I would look into getting one, otherwise your bees will starve over winter. You should fill that before you add the Flow super. Make sure each box is full before you add a new one of any type (brood box or Flow super) = all comb fully drawn out and 80% full of food or brood.