To start out, you need a skateboard to be your ginneapig. It can be a normal skateboard, or a longboard.
Step 1: Building the "planter"
Step 2: Fill it with dirt!
Step 3: GRASS!!
Using seeds is pretty easy. Just throw them down and water them perodically. Simple.
You can put an entire slab of grass down, which would be transplanted from another source, and thats simple enough. Put it down, and you're done. congrats.
Or, you can do what I did. I didn't have a slab of grass I wanted to get rid of, and I didn't want t buy seeds, so I decided to weed my garden beds and plant all the patches of grass on my board. Its slower, but eventually, the patches will grow and spred like weeds and soon cover my entire board.
Whatever you choose, Kepp the board out in a sunny location and water it eveyday. You can control every aspect of this grass very easily so yopu can't use the same excuses as for you gross brown lawn.
Be patient, trim it when you need to, and enjoy your new green mode of transportation!