Depending on the size of your website, how many visitors you have, the content that you create and the quality of said content the answer differs. A big website will see results rather quickly, perhaps even within a few days. Before you change your SEO strategy because you think it is inefficient you should wait at least a week but up to a month.
It is not necessary to know how to code but for certain special features it is useful to know the basics of code. An essential understanding of coding will help you understand how SEO works.
When a search engine such as google crawls over your text they will index certain things. The indexed content will appear on the search machine and therefore be visible for your potential visitors. However you cannot choose what content will be indexed and what won't. Think about that while you create your content.
Just because the amount of visitors on your website increases doesn't mean your sales have to increase as well. The content you create should be aimed at your customers.