If I ask any question which is too basic, sorry I am still learning all of it.
Let’s say that I want to add snippets from a website that has some good one to add nice effects to pictures from my banners or any images that I have throught my store ( I am using the DAWN THEME)
WEBSITE with CSS Snippets URL: https://www.sliderrevolution.com/resources/css-gallery/
I checked broken information on youtube and many other websites that for someone learning are very incomplete and never give out the complete info. for instance, someone says that I should create a custom.css file and then paste my css snipprts there and also link it to my HTML file (example : theme.liquid) - IT didn’t work 
I spoke with someone on shopify that told me that if I access my theme.liquid - HTML file, I can find the image I want to give the nice effect and then paste the snippet css code in there (above the image) then also add some kind .liquid code to make it work, I didnt find any example showing me anything that I could follow. Also there is a lot of material just with old themes and not much with the DAWN theme.
I am also trying to LEARN and add to a store the resources of - greensock : https://greensock.com/docs/