Try to hear the difference between the flap /ɾ/ (like in "butter" - American accent) and a normal /t/ . You can slow the video to 0.5x speed to isolate the sound.
Best for: Visual mouth diagrams. Rachel uses a mirror view to show you exactly how to shape your lips for vowels like /ʊ/ (book) vs /u/ (boot). Youtube - Ipa
4 minutes