Take dark frames at the exact same exposure settings & length you used when capturing the images... simply put the cap over the front of your scope & snap away, usually I do this at the end of my image capturing session. This is when the camera/sensor is at it's hottest & thus, you are likely to capture any hot pixels...
Dark frames are then loaded to Deep Sky Stacker (another windows based free program) at the same time you load your light frames (image shots).
Flats can be done a number of ways & technically, can be done at any time or settings... I don't use them, I probably should but, I don't... I have purchased an led tracing board with the intent of trying to use it to capture flats but... I haven't done so yet...
Google 'taking flats in astrophotography' & you'll turn up a myriad of ways of doing them & explanations for what they are for...
Bias frames, I've never done them & despite reading up on them, don't really understand what they are for either...
Sorry, forgot to mention Bhatinov mask in earlier responses... yes, you definitely should have one for getting sharp focus both for deep sky and planetary/lunar.
There's a chap on ebay who 3-d prints them in Melbourne... his prices are exceptionally good & if he doesn't have what you need, you can chit chat back & forth & he'll make one for you... usually just needs some measurements from your scope... don't buy one commercially, it'll likely cost you 3 - 4 times the price...