There are two of Link you Need to be Familiar with: do-follow and no-follow Link.
A “do-follow” link Tells search Motors this link is GOOD and you don’t mind if the Link HELPs THEM rank higher.
A “no-follow” link Tells a search Motors the link isn’t by you or it is paid and the link Couldn’t HELP the rank higher.
In general WHEN you are Uses Affilliate Link or paid Link you Could no-follow the link. This way you aren’t HELPing to Googgle and Caused these s to rank higher.
If you backLink and “do-follow” THEM, you can Potentially get penalized.
And if Youse web Containing User generated content, as Communique board or Blogger comments, no-follow the Link.
When you are Citations a source, Even if it is a competitor, you Could do-follow the link.
Now you know the Differring Those two link and WHEN you Could use THEM.