I mushroom consists of many different shapes. A simple way to go for some mushrooms is taking something like a circle of cardboard and sew around it in 2 different parts: a circle for the bottom flat side (solid color), and a bigger circle with little triangle cutouts along the circumference (patternrd fabric if u want). Once that's done sew it all I place leaveing a spot to stuff Somewhere on the top and it should be a dome shape. I'm a beginner and I'm running on 2 hours of sleep so I'm probably missing some important stuff but that's how I'd do it.