Advanced WordPress Background (plug-in) problems

Hi,
I’m new to this so be kind with me ??
I installed the plug-in “AWB – Advanced WordPress Background”, for parallax and scrolling effects and I have some questions I hope some of you will be able to answer.

Keep in mind that:
-I’m not a dev but:
-I’m open to modify some parts of the code, will watch some tutorials or follow what some of you will say ??

-Storefront theme
-NOT Gutenberg editor (for now)
-localhost with MAMP on MacBook

Questions:
1) Where I can apply that effect? Only in the first part of pages?
2) When I use AWB and apply scroll + parallax mouse effects sometimes only one of them will work, is that a problem of the plug-in or I have to do change some settings?
3) When I use AWB and upload the image it is 1280×720. Then in the real page is really really small and thinner, not resized or stretched, seems that I can see only a slice of the image!

Tried to mess something up is the code that it generates but nothing…

Thanks to everyone will respond! ??