The problem isn't with learning it, it's with finding out which one to learn.
Assembly differs according to your CPU architecture, all right. Most PC CPUs are built with the x86 architecture? Fine.
From my understanding, there's still a multitude of different versions. NASM? MASM? What's the difference between these? How many more of these are there? Why are there more than one for one architecture? Which one should I learn?