I am very confusing with PostBack and Partial PostBack, Can you please explain both of these?

A post back occurs when you post ALL of the data back from the Web Form to the server. A partial post back, just returns a limited chunk of the data from a Web Form back to the server.

Have a look at How to write your own partial postback in ASP.NET 2.0[^].

Excerpt -> "At the heart of the partial post back construction is the XMLHttpRequest, a DOM API. It can be used inside a web browser scripting language, such as JavaScript, to send an HTTP request directly to a web server without having to reload the entire page and handling the response from the server again within the scripting language. This data, in the form of XML, can then be used to manipulate the page elements on the client side.

On the server side, we implement an HttpHandler to handle the request and pass back data in a valid XML form.

By doing so, we are preventing page refreshes and roundtrips of static data and content in the web pages"

This indicates that a partial postback occurs when you are refreshing a part of the page using some mechanism.
A full postback would be when you refresh the entire page.

Partial postback is a technique where you dont post the whole data to the action page and thus the current page is not changed/removed.This is implemented using ajax where only a limited data is posted back like

Suppose a dropdown asks for your country name and you select it.
After then using Partial PostBack your country name is sent to server without refreshing the page and the below dropdown of state automatically gets populated with server response containing state names for that country.

However you dont see such things in your login page of various websites as they are using postback where the frame refreshes

To communicate with server we have to pass all life cycle of object is post back.

To communicate with server we dont lose the life of a object is partial post back