To install the free Affiliates plugin follow these steps:
Installation from your WordPress dashboard (recommended)
1. Select the ADD NEW option from the PLUGINS menu in WordPress.
2. Insert “affiliates” in the search bar.
3. Press the INSTALL NOW button.
4. Activate Affiliates from your WordPress Plugins menu (Access your Installed Plugins menu to check it’s listed)
Installation using the plugin .zip file
1. Access https://wordpress.org/plugins/affiliates/ and press the DOWNLOAD button.
2. Check that the affiliates .zip folder was correctly downloaded (just for zip format). If you’re using Safari and cannot get your zip file, access the General settings of the Preferences menu and untick the checkbox “Open safe files after downloading…”
4. Select the downloaded file.
5. Press the INSTALL NOW button and accept the confirmation message.
6. Activate Affiliates from your WordPress Plugins menu (Access your Installed Plugins menu to check it’s listed).
If you are using the free version you can use the usual automatic update process.