There are some languages in which orthographic symbols always denote the same speech sound. The English language, however, is not one of those.
George Bernard Shaw (British playwright and linguist) is often attributed with the assertion that the word 'fish' could feasibly be spelled as 'ghoti' as these combination of letters can also pronounce the word 'fish' under different contexts.
gh = f as in rouGH
o = i as in wOmen
ti = sh as in naTIon
You can see therefore the need for a system where one symbols = one speech sound and that is exactly what the chart above does.
The phonetic symbols each represent a speech sound from recorded languages (there are then also 'diacritics' which are used to further specify how a speech sound is realised and 'suprasegmentals' and 'tones' which are used to denote the rhythm and intonation of speech sounds)
The IPA is a fantastic tool for anybody who wants to understand or modify their speech whether they are an actor or somebody seeking greater speech clarity.
Within 'Book and Further Resource Recommendations' there are two videos shedding more light onto the IPA- there is an Interactive IPA Chart which allows you to press each symbol to hear what they sound like and there is also links to a free app called AV Phonetics in which you can both hear each of the speech sounds, read fairly detailed descriptions of how they are made and watch animations of the speech sound being realised.
Books and further resource recommendations
English Phonetics and Pronunciation Practice
I had the great pleasure of being taught by two of the authors of this brilliant book at UCL - Paul Carley and Inger M. Mees - in fact Inger very kindly wrote a message in my copy of the book in phonetic transcription.. pretty cool.
This is a brilliant resource for those wishing to modify their accents - about a third of the book explains speech processes and phonetics and the rest of the book is comprised of practical exercises for isolating and comparing commonly confused sounds. I would highly recommend this to anybody who is looking to modify their accent and develop greater clarity in their speech.
Speaking with Skill
Speaking with Skill was written by Dudley Knight (he is the 'K' of KT Speechwork). He is one of the most respected voice and speech trainers in America. This book is aimed at actors and dialect coaches and offers practical exercises in developing control and awareness over your speech organs. The concept of Vocal Tract Posture (or Oral Posture) is examined in detail - this is work that is vital for accent work.
Accents of English
Accents of English is a trilogy of books written by J.C. Wells who is the creator of "lexical sets" alongside various other tools used within phonetics. The first volume shows how accents vary not only geographically, but also with social class, formality, sex and age and talks in detail about "Received Pronunciation" and "General American" accents. Volumes 2 and 3 examines in greater depth the various accents used by people who speak English as their mother tongue: the accents of the regions of England, Wales, Scotland and Ireland and of the USA, Canada, and West Indies, Australia, New Zealand, South Africa, India, Black Africa and the Far East.
15 minutes of speech sounds in an MRI machine
This is a link to a video of people speaking, singing, rapping and beatboxing in an MRI machine so we are able to see what is happening in their mouth.
Erik Singer on Oral Posture
Erik Singer is a world leading dialect coach. Here is is explaining how 'Oral Posture' works and why it is so important for dialect and accent modification work.
Further Erik Singer videos
This video is a whistle-stop tour of U.S. accents (part 1 of 3) but there are also links here to his other Wired videos where you can see him analysing film actor's accent work, talking about idiolects and fictional languages.
The Glossonomia podcast is a gloriously thorough phonetics and accents podcast presented by Phil Thompson (co-founder and 'T' of KT Speechwork) and brilliant dialect coach Eric Armstrong. Most episodes last over an hour and focus on just one phoneme and it's allophonic variations so this is very thorough and may not be for those with a more causal interest but if you are looking for a lot of detail around a specific sound the /I/ sound in words like Kit, Little, Myth, Bit etc. then you can always find the episode which concerns that sound.
In a Manner of Speaking Podcast
In a Manner of Speaking is a podcast presented by world leading dialect coach and founder of the Dialect Archive Paul Meier and his episodes range from conversations with linguists and dialect coaches to solo episodes where he will look at concepts like glottalization and code switching. Paul Meier's website is also a treasure trove for the phonetics and accent fan and I can also highly recommend his book 'Accents & Dialects for Stage and Screen' in which he provides breakdowns and coaches you through 27 accents.
AV Phonetics App
AV Phonetics is by no means the only app relating to phonetics but is free and fairly detailed. As mentioned above it allows you to hear each speech sound, it describes how they are made and you can watch an animation of them being produced. There is also a fantastic glossary of phonetic terms. The speech sounds are grouped based on the manner in which they are produced (plosive, fricative, nasal etc.) rather than the place they are produced within the vocal tract.