Hello,
There are quite a few quality issues here—exposure, composition, and so on.
You also need to do some post-production—to use software like Lightroom, Photoshop and similar to make adjustments to exposure, white balance, correcting the perspective, altering the tone, etc. A photo is rarely good enough to come 'straight out of the camera'.
The only type of photo that literally came straight out of the camera was the Polaroid!
These links might be a good start to get more information.
User guide:
https://helpx.adobe.com/stock/contributor/user-guide.html
Exposure:
https://www.adobe.com/creativecloud/photography/discover/exposure-in-photography.html
Composition:
https://www.adobe.com/creativecloud/photography/discover/photo-composition.html
Learn and support:
https://helpx.adobe.com/support/stock-contributor.html
It is also important to think about the commercial value of your photos. How will they be used?