I have an app and also a Youtube Channel:
An app that I have been using is called "LingoDeer". This app not only teaches you how to structure sentences in Korean, but it also has you record your voice to compare it with the Native Speaker. The app goes through courses, and even has the option to review everything you learned. It's completely free and has a very nice interface. You can find it on the app store. This includes zero in-app purchases.
The second recommendation is the Youtube Channel "Talk To Me In Korean". It goes over a lot of words, including how to pronounce them, different meanings, why we use them etc. They have Native Speakers to explain these things, and the videos are very easy to follow. I hope this helped.