Okfred requests a block of memory big enough to hold the string "David" plus 1 by calling the malloc() function. This memory is allocated in the heap. The function strlen() (from <string.h>) returns the length of "David" which is 5. It does not include the terminating '\0' so the + 1 handles that. The variable Fred is now set to point to this 6 byte allocated block. The string "David" with a terminating '\0' is written to this block, character by character. This is a long winded way to assign a string as there are functions in the <string.h> library that do this but it gives a basic idea. The second character of this block is subsequently overwritten using the address *(Fred+1).
Note that when you increment a pointer or offset (like I did with *(Fred+1)), the pointer address is changed by the size of whatever it points to. So in OkFred++, it increments by 1- the size of an 8 bit character. If it were an int * then the pointer would alter by the size of int which is normally 4 bytes. You can see this with the array b that holds two ints. The variable int *Ptrb points to b (which is the same address as b[0]). Incrementing Ptrb now points it to b[1].
I've used the address operator & to give the address of variables. This is not needed for an array name. The addresses b and &b are the same value. This isn't true for individual array elements such as b[0] and &b[0] though. If you print b[1] you get the value stored there not the address!
On the next page : Example 1 listing
