So they work in specific ways and in the x86 chip there are built in high speed memory locations called registers. These registers are used for data being passed in from memory, or other places to be manipulated, and then passed back out into memory or other places. Its kind of like you got to put the information in specific spots it can directly get to and then setup and call the instruction. What the above example means is mov into register eax the hex value 1. The comma separates the operands.
Registers have different sizes, since the registers the cpu's evolved over time.
And so it has been with the x86 registers. The newer general purpose registers are much more general. In past days specific registers had certain agendas but these were actually limitations with the cpu. Now days the general purpose registers fall into three classes. The 32 bit general purpose registers, the 16 bit general purpose registers, and the 8 bit register halves.