Introduction threads are popular these days

. Welcome to the forums!
Hmm, it's difficult. I've played IL2 on the PC before, so I could jump to realistic right away, but I've no idea how it feels for someone with no experience.
I think the best thing to do (since you'll eventually want to play Realistic) is just go through the campaign on Realistic.
Here is a thread about sensitivity settings for different aircraft. It's pretty important, since it's very tricky to fly with sensitivity full.
What will happen to you:
- You'll stall. Probably a lot at the start, especially if you haven't set your sensitivity yet. Adjusting the sensitivity will almost eliminate this problem, without losing much of your rate of turn.
- You'll spin. Not too much I think, but it'll happen. You can follow the on-screen instruction to get out of it. These basically come down to this: ailerons (roll) in direction of spin, rudder (yaw) in opposite direction of spin.
- You might not hit a damn thing. This might be the only reason to start on arcade a bit. It's tricky to shoot an aircraft in flight, since you have to aim a bit in front of it to actually hit. In arcade you'll see a 'crosshair' in front of your target, indicating where you have to shoot to hit it. This problem will be very annoying at the start, but you'll get used to it.
- You might get shot down, a lot. In multiplayer that is. When I started playing IL2 on the PC I couldn't see anyone coming, and got shot from every angle possible. Just ignore this, keep on practicing and don't give up. You'll get the hang of it. And remember: no one is keeping track of deaths.
I'm not sure if this is what you wanted to hear, and after reading this again I'm wondering why I actually wrote this. It sounds like I'm trying to scare you away with all this doom-talk. I'm not. Once you get the hang of it it's the most glorious and memorable experience ever (sort of..). Please do not feel intimidated

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