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We all pulled our hair out with calibration at some stage. It's ok once you know how to do it but the first time there is nothing trivial about it. But it is worth your learning because calibration will unlock all the details in your data that you wouldn't see otherwise.
Here's a short practical way without going into too many details to get you started.
Let's say you shoot 10x5min subs.
With the scope at exactly the same focus and temperature you shot your subs, plug your scope and you can now shoot 10 dark frames or more of 5min then combine them into a master dark.
Next shoot let's say 40 flats of probably 0.5s or whatever duration will give you approx 1/3 of your camera full well. So if your camera is a 16bit camera, shoot to reach 10k or 20k ADU. Combine them into a master flat.
Finally shoot 80 bias at 0.001s or the shortest exposure your camera will give you. Then combine them into a master bias.
Now you have three masters: 1 dark, 1 flat and 1 bias.
You need to subtract the master bias from your flat.
Then for each or your sub you do the following pixel math:
calibratedSub = [originalSub - MasterDark]/[MasterFlat-MasterBias]
Various programs will do that. I use CCDStack.
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