How to make a website live??

You do not change the URL to make a site live. You have to have a host that provides the server for your site to be live.

Ok so first things first, have you installed WordPress properly?

The website was all finished and it was installed

A few things make a wordpress site live:

1. Domain name that points to your server IP
2. WordPress install and database that is set to the same URL or domain name e.g. https://www.yoursite.com

If you hanged the URL in you control panel incorrectly that is why you cant login anymore. A fix is available directly in your wordpress database.

This can usually be accessed from your hosting control panel.

What is your doamin name/URL?
You need to check in the wordpress database that it matches.

See here for a similar discussion:
https://www.ads-software.com/support/topic/change-url-in-existing-database?replies=4

how to make a website

As per the Forum Welcome, please post your own topic. Posting in an existing topic prevents us from being able to track issues by topic. Added to which, your problem – despite any similarity in symptoms – is likely to be completely different.