This will go over addressing and how to use spaces in memory to store data.
Any time you see a $ in a line of code, whatever number is connected to it is an address not a value.
Whenever you address, you should use 16-bit numbers. Otherwise things can go wrong.
Storing
You can store a value at a space in memory with the STA command like:
STA,0000000000000000
which stores the value in A at 0000000000000000 in memory
Loading
You can load a value at a space in memory with the LDA command like:
LDA $00000000
which will set the A register to whatever value is at memory address 0.
This can be used in almost any command!
For example to set a pixel to a color defined by memory you could do:
PXL $00000000
or similar.
Any time STA or LDA is mentioned, STY LDY STX and LDX can do the same thing but with the Y or X registers as seen in their names.