A dark spot that stays in the same place from shot to shot is usually dust on the camera sensor. Less commonly, it can be dirt on the rear element of the lens.

To check, take a test photo:

• Use a very small aperture (high f-number)
• Zoom in if possible
• Aim at a bright, plain background like the sky or a blank wall

Sensor dust becomes much more visible at small apertures.

To tell sensor vs. lens:

• Swap to a different lens
• If the spot remains, it’s likely on the sensor
• If it disappears, clean the lens, especially the rear element, with a proper lens cloth

How to fix it:

• Try the camera’s built-in sensor cleaning function first
• If that doesn’t help, have the sensor professionally cleaned
• As a beginner, it’s best not to wet-clean the sensor yourself unless you know the correct procedure

So the most likely explanation is sensor dust, and the safest solution is built-in cleaning first, then professional cleaning if needed.