Learn three more sounds: D (duh), G (guh), and short O (ah), and notice how differently each one feels.
Three more sounds: D says duh, like digging with a shovel. G says guh, from the back of your throat, like "go." O says ah, like an octopus with round, wide arms.
Duh, guh, ah -- feel where each one happens in your mouth.
Mastery looks like: They can produce the D, G, and short O sounds and sort a few familiar words correctly among the three.
Common stumbles: Confusing the similar back-of-mouth D and G sounds; saying the letter name "oh" instead of the short "ah" sound for O.