The picture is self-explanatory: By going over a boy's features we can easily learn the English diphthongs. Remember there is one more diphthong which isn't shown on the picture, /ʊə/ as in tourist or poor.
As Cristina herself suggests, to make sure of the correct pronunciation of the diphthongs you can visit the English File online site or use one of the online pronunciation dictionaries that you can find here.
