Help with CSS

I just started using wordpress and I am also taking a web design class. I am a photographer and I am trying to set up a portfolio style website for my photography and I am finding it difficult to veer away from the themes set up and make the website look more like how I want it. I need help but I just dont know where to go and how to edit my page to customize It.

I am not familiar with html/css/js as yet however I am taking a class and it is quite easy for me to learn on the spot and find out the codes that I need. However, I just dont know where to put all of the css codes and what not. Where do I input all of the codes?

I am trying to get my website – amritmanojphotography.com (this is it’s current state) to look something more like this https://www.joeyl.com/

any suggestions or ideas?
thanks in advance!