The key to learning interior design is to see if you are interested. If you are interested in this piece, congratulations, it means that you have taken the first step towards your dream. In view of your present situation, learning interior design courses should start with the most basic hand-drawing. Hand-drawing is an important way to express designers' design ideas and talents, but the essence of interior design course is interior design principles. If you want to be an excellent designer, you must have your own design concept and personal design style, so design principle is the core and essence of interior design course.
In addition, if you want to learn interior design well and become an excellent designer, I suggest you find a formal and authoritative school to study. I'm also studying interior design now. I choose the Interior Design Training Center of School of Mathematics and Statistics, Sun Yat-sen University. The curriculum is reasonable, targeted and practical.
Search online for "Interior Design Training Center of School of Mathematics and Statistics, Sun Yat-sen University", and the first one is them.