Actual sub-frames (pictures of the object you're capturing) go into the lights folder. Dark frames are calibration shots, usually taken with the lens covered, once the telescope has reached operating temp, and used to subtract sensor-noise from the stack. I don't know if Seestar offers a way to do those automatically. I actually don't know anything about Seestar and what they provide, but flats and bias frames for my Dwarf Mini were provided from the factory, and there's an option in the control app to capture dark frames.

If you don't have any of those things, you can get a script that does the stacking without them. Go to the "Get Scripts" menu and look for the OSC_Preprocessing_WithoutDBF script (or something like that). There are other scripts available out there, too, many made by the community. You might be able to find one that's dedicated to your telescope model. I suggest searching for people that have the same hardware as you and asking what they use.