What is the primary book used

There isn't one. Most people don't learn this stuff by reading a book.

The best way to learn is by looking at actual assembly code, then research what each instruction does. I wouldn't start with actual compiler generated code. Being computer generated it's often quite messy and obviously undocumented. Best to start with easier to read code like the example I've included below — a simple "print Hello World" in CISC, then in RISC.

Notice CISC uses mov, int and xor, while RISC uses mov, ldr, and svc. You should look those up in a manual (plenty of free ones online) but in simple terms:

• mov: move memory from one place to another. RISC and CISC have the same instruction but but they're not identical
• int: means interrupt, essentially stop execution (for a moment) and hand execution over to other software
• xor: modifies a value (an XOR operation)
• ldr: is "load register", it loads a value from elsewhere in memory
• svc: means "supervisor call" which, is used in much the same way as int. The code is asking the kernel to do something (once to write to stdout, and once to terminate the program).

section .data
    helloWorld db 'Hello World',0xa  ; 'Hello World' string followed by a newline character

section .text
    global _start

_start:
    ; write(1, helloWorld, 13)
    mov eax, 4          ; system call number for sys_write
    mov ebx, 1          ; file descriptor 1 is stdout
    mov ecx, helloWorld ; pointer to the string to print
    mov edx, 13         ; length of the string to print
    int 0x80            ; call kernel

    ; exit(0)
    mov eax, 1          ; system call number for sys_exit
    xor ebx, ebx        ; exit status 0
    int 0x80            ; call kernel

.section .data
helloWorld:
    .asciz "Hello World\n"

.section .text
.global _start

_start:
    ; write(1, helloWorld, 13)
    mov r0, #1                  ; file descriptor 1 is stdout
    ldr r1, =helloWorld         ; pointer to the string to print
    mov r2, #13                 ; length of the string to print
    mov r7, #4                  ; system call number for sys_write
    svc 0                       ; make system call

    ; exit(0)
    mov r0, #0                  ; exit status 0
    mov r7, #1                  ; system call number for sys_exit
    svc 0                       ; make system call