NametableBase equ $20 ;label referring to a constant
VRAM_ADDR     equ $2006 ;label referring to a memory address
VRAM_DATA     equ $2007 ;label referring to a memory address

LDA #NametableBase   ;without a # this is interpreted as a memory address like any other number would be.
STA VRAM_ADDR
LDA #$00
STA VRAM_ADDR

LDA #$03
STA VRAM_DATA