The short answer is that all "affiliate" relationships must be disclosed in plain text on your website on every page where you get any sort of compensation from anyone, whether monetary or free products. I personally recommend including the disclosure on every page.

NOTE: A hyperlink to your affiliate disclosure is no longer enough. You must have the text as well.
 
Below, you will find the pertinent links from the FTC as well as some useful examples.

https://www.ftc.gov/sites/default/files/attachments/press-releases/ftc-staff-issues-guidelines-internet-advertising/0005dotcomstaffreport.pdf

https://www.ftc.gov/system/files/documents/plain-language/bus41-dot-com-disclosures-information-about-online-advertising.pdf

https://www.ftc.gov/sites/default/files/attachments/press-releases/ftc-publishes-final-guides-governing-endorsements-testimonials/091005revisedendorsementguides.pdf

Did this answer your question?