HTTP  is used to request resource from server. It has two version 
  1. HTTP 1.0
  2. HTTP 1.1
HTTP 1.0 is older version, in this client gets disconnect after every request to the server and then it have it connect again for new request. But for HTTP 1.1 once connection stablished then it  remain connected, once the session expires.
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Now there are several HTTP status code which tell us the server response.(like 404, 200, 301, 302, 500, 502 etc)

200 :----- is used to show  the connection stablished and what client is requesting , the server has .

301, 302 :------ is used for redirection of  URL, means if it success then there must be a HTTP(200) ok/success connection. example used in login page because once it get username and password the it redirect to another URL

404 :------- it is not found HTTP request

502,501 :-------- it is server error or unreachable respond 
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HTTP methods are used to request,(perform) different types to function through web server.
There are eight HTTP method namely GET, HEAD, PUT, POST, PATCH, TRACE, OPTION, DELETE.

GET (read):------- method is used to request resources from server 
POST(deposit):-------- method is used to deposit data over server. ex -  used in login ,comment section, etc

this two are mainly used and this two are very much  useful for us .