How Do Search Engines Work?
Search engines will visit your store periodically - this process is known as "crawling". They will add some of the information they find to their index, and then use that information to help determine where you should be ranked for certain searches. The details you enter in the Marketing > Search Engine Optimisation section of the control panel are only one small part of Search Engine Optimisation and there are a large amount of factors that effect your overall ranking, such as your domain name, the number of links pointing to your store, the quality of those links (i.e. how relevant and well-ranked the website linking to your store is) and much more.
Search engines can be slow to update their rankings and it may take several weeks or months before your store begins to show up. You can potentially speed this process up by submitting your sitemap to Google, or bypass the process entirely by uploading your products to Google Shopping.