Seo Confusion

In the end, when you are doing seo, are there any free me? Most of them are a few hundred monthly fees, and accompany the book. And now I want to get a Chinese e-book that the top 100 Hong Kong people on google can find English explanations, I I found some keyword tools, but they cost hundreds or seven. I'm afraid that the e-book will sell well, and it will also accompany the e-book, not to mention that it will not sell well. Do you have any suggestions or articles? or method