The three main parts: the upper receiver, the lower receiver, and the handguard (also called the rail or forend). Use them to find everything else.

On the lower receiver:

• Buttstock and buffer tube: the stock rests against your body. The buffer tube houses the buffer and recoil spring.
• Grip, safety selector, and trigger: you control and fire the rifle here. The trigger guard helps prevent accidental discharges.
• Bolt catch and release: on the left side; locks the bolt open or releases it.
• Magazine release and mag well: the release is on the right side and drops the magazine. Call it a magazine, not a clip.

On the upper receiver:

• Charging handle: loads a round from the magazine into the chamber.
• Forward assist, ejection port, and dust cover: the forward assist helps seat stubborn rounds, and empty brass exits through the port.
• Picatinny rail: where you mount scopes, red dots, and iron sights.
• Bolt carrier group (BCG): inside the upper; loads fresh rounds and clears empty cases.
• Muzzle device: at the tip of the barrel; generally reduces felt recoil.