This is a tablet. It plugs into your computer and you use that pen to draw on the tablet's writing surface. Unlike a mouse, a tablet can be sensitive to pressure, so depending on how hard you press down with the pen, your line will get thicker, darker, or whatever you tell it to do (Photoshop can do some wacky stuff with its brush settings).
To make edits really really detailed, zoom in a lot and use a one-pixel brush - you get better control.
To keep lines smooth, whether it's fabric or not, zoom in a lot.
Yeah, I like zooming in.