Korean GG has a lot of potential, but because of some bugs in its programming, you may want to make sure they have updated the app before purchasing full access.
On the first page, you will be able to tap on every possible combination of Korean consonants and vowels, receiving audio pronunciation by native speakers and an example word. You can also dive deeper into every jamo (the characters that make up the Hangul alphabet) to learn their pronunciation, stroke order, origin, and example words. Moreover, the app offers information about the history and principles of creating Hangul and includes mnemonic devices to support your learning.
Korean GG is a comprehensive reference guide, but its in-app courses are probably not as effective as in other apps. There is a section on “text reading,” which contains dozens of phrases that incorporate a specific jamo, but the audio recording doesn’t allow much time to repeat after each sentence. Their course sections are useful tools to familiarize yourself with Hangul, but are probably not enough to support you in learning to speak the language.