If you want to learn quickly, forget about music management first and find a simple song, such as "Zebra Zebra", "Those Flowers", etc. Just press the chords with your left hand and brush with your right hand. When you hear all four strings sounding accurately and with a full sound, you can learn the right-hand rhythm. There are some basic rhythmic patterns. Broken chords: (41) 323, (421) 323, etc. Strumming: down (down up), down (down up) (empty up) (down up), etc. There is also syncopation, a very lively way of playing. You can start by breaking down chords. Rhythm must be practiced frequently and become a kind of inertia, otherwise it will be easy to get distracted when combined with singing, which is the reason why your playing and singing are out of sync. Practice the playing first and then sing.