Begin with nios by writing on a lcd

hi

i've successfully write on my character lcd, and use different pio for controling some vhdl functions around to count some frame and display the count value in the lcd

now, i would like to control a memory to store pixels values inside it and then make the nios processor able to read these values

i heard about the dma but haven't yet understtod how to use for controling an external memory as a SRAM one

any idea how to do ?