share point extractor set up

can someone please explain the this procedure for me with details ? because I got really confused. so first we register an app  and create a client secret and add api read all permission n Microsoft azure, after that we create an app in SharePoint  and we add the “permission request” to it later. after that what is next before downloading the extractor ? how are the two apps linked ? I saw someone at my work using Microsoft graph to link them but did not understand the logic behind it. and if this how they are linked , how ?  when in the Microsoft when doing the post each app dose not mention the other