Inserting Links into posts

Hi

Could anyone please. I am trying to insert a link in my blog post to go to for example an amazon product. I get the html code from them and insert it into the box. When I publish the post it seems to automatically default the name of my website in front of the post and then the link, which makes the post try to access a page on my site. This also happens whenever I try to put a link into text. It seems like a default of some kind, but I can’t figure it out.

Has anyone any ideas.

Thanks