To form the voiced "th" sound in American English, stick out your tongue so that your upper front teeth rest on it very gently. This sound must be continued, which means that you will need to keep your tongue and upper front teeth touching while you say it. Try not to open your mouth and separate your tongue and teeth. This will be the hardest part. You use your voice to say this sound, which means that if you place your hand on your throat when you say it, you should feel your vocal cords vibrate. You will also hear your voice.