Go to the bookstore to buy related books, from basic learning to higher education. The biggest advantage of books is that you can learn when you are disconnected from the internet and power.
If you want to learn this, it must be related. For example, if a friend is engaged in this industry, you can take this as a starting point, contact knowledgeable professionals and give some advice.
Read more online renderings, schemes and construction methods. When you have time, go outside and look at the buildings, and see their styles, materials, shapes, colors, textures and so on. Even depends on the surrounding buildings, greening, understanding of his history and so on.
In short, we should understand, refine and taste the renderings or what 3dsMax will show in interior design.
As for studying for free, Peng Zhong thinks it is almost impossible to study indoors. Unless you have a special talent for learning this. Otherwise, even if you spend money to learn, you may not be able to meet the needs of interior design after learning. The key is personal practice.