I would like to create a full HMTL Landing Pages within Web Studio > Cloud Pages. I have my HMTL code and a CSS file. Where do I need to store my CSS file to be able to use it when creating my HMTL landing page?
Within your Cloud Page collection, you can create a Code Resource:
After you fill out the name of the code resource, you can select the type, which in your case will be CSS:
You will now be able to paste your code into the editor, and reference the stylesheet with the url you declared during the creation wizard.
Read more about Code Resources here.