An Introduction to NoFollow and DoFollow links
This training is directed at anyone who uses affiliate marketing links in their posts or pages. Mostly for entry level folks but some intermediates might also benefit from a review of why using “nofollow” attributes in your posts is important.
To begin, the term “nofollow” is an HTML attribute which tells search engines that your hyperlink should not influence the link target's ranking in that particular search engine's index. Why is this important? It is intended to reduce the effectiveness of search engine spam, which improves the quality of the search engine's results. What this means in layman terms is that the search engines will not be able to follow your “nofollow” links. Only a human clicking on your link will be able to reach that link. Google has indicated in the past that they will not weigh a link that isn't “nofollow”, but it is considered best practice to make your affiliate links “nofollow” links.
Next, How to Add a No Follow Link