Brand new Ender 3 does not extrude any filament during printing I bought an Ender 3 two days ago and assembled it today. I think I did it properly, tested the movement of all axes which works for all axes. Then I performed the calibration as described in the manual. I used a piece of paper and adjusted the bed until it barely fits underneath the nozzle for all four corners. Afterwards, I wanted to print my first model so I selected the cat from the usb stick which came with printer. And now comes my problem. I let the printer run for 15 minutes. It moved and moved and moved but there was no filament on the bed. The nozzle and bed were heated properly. The one thing which I noticed was that the stepper which feeds the filament turns for like 30° and then flips back: to me it looks like the filament can not be fed in. After canceling the print the extruder moves back to the home position which is like 5 mm off the bed and then suddenly the filament flows out of the nozzle.
What part of the configuration I'm missing?
I am a fairly new user of an Ender 3 and had similar issues on a couple of occasions.

The main reason was as @0scar suggested - the nozzle was too close to the build plate preventing the filament from exiting - and the back-pressure was causing the filament to jump back, giving the extruder a "shudder" as it slips on the filament. Lower your build plate as suggested by @0scar. The paper should only just drag.

The fact that filament oozes after the hot end/print heads moves to home suggests you don't have a blockage... but you will if you don't adjust this.

It is better to have the nozzle slightly too high, so the first level does not stick and gradually raise the bed up while you are running the test patterns. Only turn the adjustment knob about 1/8 of a turn before checking - you are dealing in tenths of a millimeter here. Also remember that changing the front setting is going to change the back settings too because the plate will tilt.