What does the params rails object consist of.

What does the params rails object consist of.

I know I can access GET and POST parameters through params object. I am
though reading the getting started guide and cannot realize what does the
params[:post] comes from. How does the params object is been formed in
each case GET and POST.
@post = Post.new(params[:post].permit(:title, :text))
http://guides.rubyonrails.org/getting_started.html#the-first-form