<p>I bought an Ender 3, and after assembling it following the description and some YouTube videos and after correct leveling, I printed the test dog gcode on the micro SD card that comes with the printer. PLA 1.75&nbsp;mm. Attached the image of the printing result. What went wrong? I didn't change or modify any settings what so ever, I just assembled the printer, and printed the test dog. Please help me, I am a beginner in 3D printing. </p>

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This is an extreme case of repeated layer shifting in the Y-carriage, which can come from some pieces related to the carriage. Luckily for you, they are easily fixable.
The Ender3 Y-carriage has an eccentric nut to adjust the force the wheels press down on the V-slot. Adjust it (most likely loosen them a little) so it moves smoothly when the motors are off, but keep it tight enough so it does not tilt.
The belt in the Y-carriage might be loose. Tighten it till it gives a nice ring when struck.
Check if the gear on the Y-motor is tightened down correctly. If it slips or wriggles, the backlash results in the layers shifting.
The Ender3 has the cables to the gantry and the bed running across each other and quite open. Make sure nothing can be caught in them.
Make sure the gantry is parallel to the bed and stays so in moving upwards - adjust the wheels as needed.
To ensure this, make sure the lead screw is orthogonal to the gantry. Level the bed afterwards. You might need to adjust the motor mount, possibly by shimming.