Where are the function variables defined?

[easyupdo]

hi sir：
There is a syntax like this in the script.“hi def link cCustomFunc Function”.I know this means cCustomFunc==Function. what is my question? where defined the Function？My ultimate goal is to customize the color of the Function. By the way. sir. How to highlight user-defined data types and Variable alias when they are used. At last,Why is my variable not highlighted?

There is my vimrc:
{
let g:cpp_class_scope_highlight = 1
let g:cpp_member_variable_highlight = 1
let g:cpp_class_decl_highlight = 1
let g:cpp_experimental_simple_template_highlight = 1
let g:cpp_experimental_template_highlight = 1
let g:cpp_concepts_highlight = 1
}