Application layer is the upper most layer in OSI and TCP model. It is the layer which is responsible for giving interface between two nodes for an application. there are a lot of protocols which are categorized into application layer.
6. FTP ETC.
In DNS ie. domain name system/service/server , As we know that every server has its own ip address . but it is too difficult to remember the ip address of every server . so for solution of this problem , DNS was introduced. with that computer can communicate by the URL OR URI of server.
in HTTP, whatever we are communicate by client (browser) and server or peer to peer , all are because of HTTP.