This calculator has three memory registers. For entering a value into a memory register, first enter the value, press [ENTER], then enter the register number and press [STO].
Example:

Save 15 in memory register number 2:

15 [ENTER] 2 [STO]

Suppose that in memory register 1 you saved the number 10.

1 [RCL] recalls 10 into X register.

Another example:

20 [ENTER] 3 [STO] You save 20 into memory register 3
15 [ENTER] 3 [STO+] Then, you add 15 to memory register number 3
12 [ENTER] 3 [STO-] then, you substract 12 from memory register 3
3 [RCL] then you recall the contents of memory register 3 (currently 23), and load this value into X.

[CLRG] means Clear All Memory Registers