This is Oliver, he’s a real “connoisseur” of grass.  It took about one month to grow this.  Very simple:  Fill cup with sand, press oat or wheat seeds in just below the surface.  Mist and cover with plastic wrap.  Set in the sun.  When seeds sprouts, sprinkle a bit of potting soil over.  Keep evenly misted.  Picture 4 was after 2 weeks, 5 a week later, then finally 6 weeks.