Get a tin whistle
First of all, you have to get a tin whistle for yourself. You can easily get a whistle from a music store. If you don’t want to go to a music store, you can order it online. The most common tin whistle is D whistle which plays the keys of D and G major. Moreover, C whistle is the second most common tin whistle which plays the keys of C and G major. You must buy a whistle which suits your style. The wooden fipple is commonly used by the musicians. However, if you want variation, you can also buy the whistle made up of a metal body tube.
Learn to hold the tin whistle
The whistle should face downwards as you hold it. Keep your dominant hand right at the bottom of the whistle and use fingers to play different tunes. The pinkies are not used until or unless you have to play some particular tunes. Furthermore, you have to place the tip of the whistle right between your lips instead of your teeth.
Learn to use fingers to play different notes
Please note that the standard range of the tin whistle contains two octaves. In order to play D whistle, you will have to use notes from the second D which are right above the middle C and go to fourth D, above the middle C. You can simply learn the use of fingers by following the instructions given in the book containing the music notes.
You will have to keep practicing different notes so as to master the tin whistle. After sometime, you will be able to make your own tunes.