Given that the as entry is the virtual address space of the process, what can we do with it? The as entity was made to look like a file so that you could perform file-like functions on it (read(), write(), and lseek()).
For example, if we call lseek() to seek to location 0x80001234, and then call read() to read 4 bytes, we have effectively read 4 bytes from the process's virtual address space at 0x80001234. If we then print out this value, it would be equivalent to doing the following code within that process:
...
int *ptr;
ptr = (int *) 0x80001234;
printf ("4 bytes at location 0x80001234 are %d\n", *ptr);
However, the big advantage is that we can read the data in another process's address space by calling lseek() and read().