I would recommend not jumping right into x86 and instead starting with something simpler. I learned MIPS in school. The instruction set is very easy to wrap your head around.

MIPS Quick Tutorial: http://logos.cs.uic.edu/366/notes/mips%20quick%20tutorial.ht...

A simulator that will let you run MIPS on windows/linux/mac: http://pages.cs.wisc.edu/~larus/spim.html