Can not create field when I tries to create a new doctype

Hi, Dear All
I am new to ERPNext and is learning and playing around it. I am trying to check the existing doc type and trying to create new doc type.
However, in the doc type screen, I am not able to see the section “Fields” which allows me to add the fields.
Could anyone give me some hint here where could go wrong?

It is the same for the existing standard ERPNext doc type, can not find anything there.

Add further screeshot for standard doc type:

Its in form tab

OK, Thanks…It is in the very bottom of the page…I didn’t notice it. It is not consistent as in the documentation…