Inner Circle: 6 short vowels; symbols are all single; these vowels never end a syllable.
Corners: 6 long vowels; symbols usually have ː but /eə/ also considered a long vowel in this model.
Sides: 6 dipthongs; symbols have 2 elements; the sound moves from one position to the other.
Long-short vowel pairs: Each pair shares similar mouth position.
Centre: The weak vowel also known as 'schwa'; only used in unstressed syllables; the most common sound in English.
Optional r: The letter r usually comes after these sounds; pronounced in some accents not in others.
More info:
Read full infographic: The PronPack Sound Chart
Watch: video explanation
Sources:
Audio files from: abelard.org & Forvo.com
Original code: dodecagondiv
Original code: Sound For Mouse Hover Script
Links:
Link 1: Consonant chart
Link 2: Mobile phone version of vowel chart