I’ve never used a 3d printer before but want to get one. I have a bit experience in blender but not too much. My question is: How do you model for a 3d print? For example, if I want to print a hollow cylinder, I go into blender, create cylinder and delete the side faces. If I print this, the walls will be pretty thin. Do I have to make them bigger manually? and if I do so (extrude and scale) does my slicer (cura) automatically fill in the solid part?
To answer your question (and not just recommend another piece of software instead):
Making a cylinder and deleting the cap faces makes what’s known as a non-manifold mesh. To my knowledge this means you can see the backfaces without travelling through any existing faces (in your case, you can see them by looking through the holes you made when you deleted the cap faces).
That cylinder has walls that are theoretically infinitely thin, so you should thicken them up before attempting to print it. You can do this with a Solidify modifier. You can also extrude and scale them if you like, it achieves the same effect.
Given a manifold mesh, your slicer will treat the inside (as in, the direction the backfaces are pointing) as solid, and you can change the density and infill pattern to whatever you like.
Make a few of these shapes, both manifold and non-manifold, and see how your slicer reacts when you tell it to slice them.