You could take a music theory class at school, at your local community college,...or you could ask your piano teacher to incorporate theory lessons. But you can also teach yourself by studying from books such as the one recommended or you can try one of the many free online theory courses. A particularly thorough one is this course:https://www.dolmetsch.com/musictheory1.htmYou might feel a little overwhelmed by the amount of stuff there, but take heart, you don't have to know it all. A nice feature about this course is you can actually hear the examples through your soundcard.
By the way how did Traumerei go? You were working on it recently. (And your name...are you Ghanaian?)