Django - 如何将certein应用程序专用于数据库

I've read Django docs, but I am afraid I don't really understand what is written, and what they are trying to explain. I want to know how I can dedicate one app to one database, 2nd app to 2nd databse, etc. I get the part where I am inserting new databases in settings.py, but the tricky part for me is when I have to connect apps and databases>I've read Django docs, but I am afraid I don't