hi there! things can be confusing at first but i guarantee you will get the hang og things soon.
let’s start with the basics. did you check the email with which you signed up for netlify with and confirm your email? You won’t be able to login and access the /admin
page (which is, just to be really clear, part of Netlify CMS, not Netlify)
maybe this post will help understand the difference between the two: