This sound is used in words like een (one), thee (tea) and lezen (read).
This sound is pronounced as a so-called diphthong: a combination of two sounds. It means that there is always a movement of the tongue (and/or other parts of the mouth) involved while producing the sound. Diphthongs are therefore generally long sounds. For example, compare ‘hat’ (not a diphthong) and ‘hate’ (a diphthong).
The sound ee closely resembles the vowel sound used in British English words like ‘day’ and ‘reign’. There is a slight difference, however. Start saying the sound ‘ay’ in ‘day’. Once you have said this sound a few times, you may notice that your mouth goes up and down (a diphthong). In order to make the Dutch sound, you should do the same thing, but your mouth should make less movement, so your chin should be higher at the start (picture 1). You should almost end in the sound ie (exercise 2). So again, your cheeks should be far apart and end in a grin (picture 2).
Now you should be able to pronounce the sound ee.
! Please note that the sound in the article een (a/an) is pronounced differently (see exercise 5).