I have to scroll down my webiste to make my background images appear and also it takes a while, how could i fix that by javascript by adding some kind of loading screen before displaying whole website
here's my website: https://donajsky.5v.pl/
You can create something that loads the page on the background and show the user a loading screen, but that might not be a good idea in terms of user experience and SEO.
I´d suggest to improve loading speeds by reducing the size of your images (space6.jpg for example is over 3 MB) so that your site loads quicker.
You can also take a look at lazy loading. The page then only loads the visible images. When the user scrolls down, more images are downloaded in the background. See https://developer.mozilla.org/en-US/docs/Web/Performance/Lazy_loading for example.