Th makes a voiced or unvoiced sound, depending on the word. The only difference is that one is voiced, and the other is unvoiced.
To make the unvoiced th sound, exhale through your mouth (do not hum). As you’re exhaling, slowly bring your tongue towards your teeth, until your tongue is lightly touching your teeth, and you can feel air moving against your tongue. Since it’s unvoiced, it’s a quiet sound.
This is a soft action; don’t do anything forceful when saying the th. Also the th is not a short sound; make it somewhat long. (The th is a sound that is possible to hold continuously, as long as you have air in your lungs.)
Some sentences to practice the unvoiced th sound (“the” has a voiced th, but all the other examples of th in these sentences are unvoiced):
The athlete ran three thousand meters to the north.
I think the thin thief ran north with the cloth underneath his arm.
It is his thirteenth birthday today.
You can clean your teeth with a thin toothpick.
Thanksgiving is celebrated on the fourth Thursday of the month of November.
Bite through the turkey thigh with your teeth.
Thousands of thimbles protected his thumb through thick and thin when he was handling the thistles.
Through thick and thin, the two remained loyal.