And can GlobalGetAtomNameA and GlobalAddAtomA work in different processes ?

Global - all this is left over from 16-bit Windows, where different modules could be in different segments. This is about segments, not about processes. All Atoms will be inside your process only. This is most often used in window classes to register the class name. In response, you get just such an hAtom.

ADD: GlobalAlloc has the same prefix, but it allocates just memory within this virtual address space and not even shared between different processes. But blocks of this memory can be used by any module (exe or dll) loaded into that address space.