Welcome to cycling!
First, for (almost) all workouts you should set your trainer in ERG mode. You do that in SYSTM Settings (the gear on top right). Click on the Devices tab. You’ll see your KICKR listed. Then you’ll see either something that says ERG or Level. Set it to ERG.
What does ERG mode do? It means that the trainer will maintain the power target called for in the workout no matter what gear you’re in or what cadence you use. In practice, that means changing gears will make no difference at all. So don’t! (There are nuances relating to speed of power changes, but don’t worry about that for a while.) ERG also means that when you pedal faster, you’ll need to apply less force and when you pedal slower, you’ll need to apply more force. It’s as if the bike is shifting automatically to keep you going at the same speed up a hill no matter how fast or slow you pedal. So for workouts, use the small chain ring and the 3rd or 4th smallest cog and never shift.
Second, let’s talk about fitness tests. For Half Monty, you will ride the first part (the ramp test part) in ERG mode and suffer mightily as you get higher up the ramp. If your guess at you FTP and MAP (set it about 1.25x FTP to start) are in the ballpark, you won’t finish the ramp. You’re not supposed to. When you get to the point where you no kidding can’t continue to turn the cranks, stop. The instructions will keep reminding you and tell you what to do next.
One thing you’ll do next is switch to level mode. You do this right in the middle of the test. I suggest you use level 1 or maybe 0. So what’s Level mode? Level mode mimics climbing a hill. Level 1 corresponds roughly to a 1.5% grade. Unlike ERG, cadence and shifting matter. The higher the gear or faster the cadence, the more power you’ll generate (just like on the road). Keep in mind that acceleration causes power to jump up and then come down to a steady state. So if you shift or change cadence, power will move a lot before it stabilizes (although it will still bounce around because no one has a perfectly smooth stroke).
I think that’s enough to get you started. Ask more questions as they come up.