What is the utility of the extern keyword in c?

Man, after searching I understand that extern is to indicate that a variable has already been defined in another part of the program as a whole. For example, if you divide a giant code into 2 parts. You should tell the compiler that you are using these variables in one block (file 2) but they have been initialized in another block (code 1).

For example:

Code 1:

int count;
float sum;
int main(void)
{
    ...
    return 0;
}

Code 2:

extern int count;
extern float sum;
int RetornaCount(void)
{
    return count;
}

Here is a link that explains it better than I did: link

I hope I have helped.