Rappel is a wonderful for understanding the basics of assembly language. Initially assembly language is quite challenging to understand for the programmer as all these registers are quite confusing. Specially it becomes more difficult because the programmer is now limited to using only handful of variables where as in other languages, the number declaring variable appears to be unlimited.
After we download and run the rappel, we can see that
$ ./rappel rax=0000000000000000 rbx=0000000000000000 rcx=0000000000000000 rdx=0000000000000000 rsi=0000000000000000 rdi=0000000000000000 rip=0000000000400001 rsp=0000000000000033 rbp=0000000000000000 r8=0000000000000000 r9=0000000000000000 r10=0000000000000000 r11=0000000000000000 r12=0000000000000000 r13=0000000000000000 r14=0000000000000000 r15=0000000000000000 [cf=0, zf=0, of=0, sf=0, pf=0, af=0, df=0] cs=002b ss=0000 ds=0000 es=0000 fs=0000 gs=0000 efl=00000202
The below is a screenshot of rappel.