The IPA chart is an overview of the International Phonetic Alphabet and helps describing and distinguishing sounds of spoken language. For standard English accents (General American, Standard Southern British, and General Australian), it's certainly useful to have in your pocket.
The interactive version of the IPA chart from the International Phonetics Association lets you search for the consonants and vowels (and more), click on them, and know how they're pronounced. I recommend you use the audio recording on top because it represents the sounds most accurately.
If you ever want to type out anything phonetically, typeit is your resource for it. It's an online IPA keyboard that allows you to type any word and copy paste it to wherever you need it. Its organized view allows you to make use of the full IPA without having to download a separate keyboard.
The Cambridge online dictionary is a dictionary and thesaurus in one. It gives explanations of various meanings of the word, any further connotations, as well as different usages and even related words. Additionally, it provides pronunciations of the words in UK and US standard English accents in phonetic and audio format.
The OED, the largest dictionary of the English language, not only holds a historical and contemporary dictionary database, but also provides free resources of various world Englishes, including pronunciation models and keys.
The IDEA or the International Dialects of English Archive is a database that holds voice recordings from a vast array of dialects. It covers speakers from over 120 countries. With some recordings, it is not an entirely accurate source of accent, however, because additional speaker information, such as other influence on speech, is not always provided.
With YouGlish, you'll find words and expressions in English from YouTube. It searches the YouTube database for clips that contain your word or your expression. Captions are provided with your word or expression highlighted in yellow. You can even switch between different clips, to see how it is used in action and across different accents. While you can browse for certain English accents, any speaker specification or background is not provided, therefore please take it with a grain of salt.
