Site Redirects is a plugin by Dolphiq. Its purpose is that allows for quick generation of 301 redirects.
A 301 redirect is a response code the server sends a browser to let it know that the resource being accessed has moved to another location. Upon receiving a 301 response code a browser will attempt to fetch the resources from the new provided URL. More information can be found on MDN.
In the Site Redirect plugin, click the New Redirect button in the top right. More information can be found on the rules documentation page.
Documentation can be found here.