Even if you are learning from the internet, you need to know and understand chords. If you will be playing by ear or from lead sheets you must understand how to construct chords and certainly start practicing playing them. I like to use Secrets of Piano Chords & Progressions by Duane Shinn. He does an excellent job of explaining how to construct all the chords you need. He also shows you a wonderful way to practice them. After working on chords, he takes you through chord progressions. By using this and analyzing songs to learn to recognize how it's used, you can become very proficient in playing from a lead sheet or recognizing what is happening in a piece so you can play by ear. Along with this book, I use several other books to supplement analysis and practical application. Once you have a thorough understanding of chords you can watch all the youtube videos and understand what they are saying!