评论源代码以了解整个项目的工作流程的最佳方法？

in private and in companies it is over and over again a problem that I or we developers comment in fact our code but generally nobody knows exactly how the code of the whole project works together. When I write my own code and the project is getting bigger I sometimes have this problem too. Although I write tons of comments, after 3 months you don't know what the whole thing exactly does, that means how the different methods and classes work together.in private and in companies it is over and over