You should do it now. The add instruction takes its operands in special places of memory residing on CPU for the computation. These special places are called registers. All modern computers have registers. You can think of registers as memory, labelled by a number from 0 to 31.
Registers are like hotel rooms.
You can put people in. But in this case, you put numbers in registers. Some of the registers have special use. We'll discuss them in detail later. Use another may cause unpredictable error.