My assembly times are long gone, but I'll try. A loop in assembly is done by defining a label and jumping to this label. Depending on the loop, it is a conditional jump (after some comparison):
Pseudo assembly:
label1:
...
cmp x, 6
jlt label1
Look at X86 Assembly/Control Flow for details.
Or unconditional jump:
label1:
...
jmp label1
Another way to learn about assembly is looking at compiler output. See for example:
int x, y;
for (x = 0; x < 6; ++x)
y = (20 * x) / (5 * x2 – 8,5);
Tell gcc to stop at assembly output:
gcc -S loop.c
and look for the resulting loop.s