typedef struct prefixName
{
char firstName;
char lastName;
} Name_t;

This creates a new name (Name_t) for the type "struct prefixName". If
you leave off "prefixName", then it creates a new name (Name_t) for the
unnamed struct with two char members.

Slightly off-topic...

but I have a question.

If you do the following in C:

struct Monkey { int i; };

Then you have to declare objects of it like so:

struct Monkey object;

But if you do the following:

typedef struct Monkey { int i; } Ape;

Then can you declare an object of it as follows:

struct Ape object; //using "struct" prefix

Or can you only do:
Ape object;

I presume that you'd still be able to write:
struct Monkey object;

but NOT:
Monkey object;