Document root [var/www/html] does not exist

Hey,

I’m fairly new in setting up a server and I’m sorry in advance for not being as techinically detailed with my problem but here is the gist of my problems.

So just 4 days ago I created my droplet for my WordPress site following this tutorial. https://www.wpexplorer.com/install-wordpress-digitalocean/

It worked perfectly at first and I begin working on the site installing a theme and got some considerate work done. Then, the very next day the site was working through the domain (which is the IP address) however the wp-admin wasn’t. Then, I tried logging into the console of Digital Ocean and it asked me to enter my username and password yet again; it basically functioned like I was creating a site for the first time again. It asked me to set up my domain (again) and I chose the same IP address for domain. However, this time the site didn’t load at all giving me the error

NOT FOUND

The requested URL was not found on this server.

Apache/2.4.29 (Ubuntu) Server at 159.65.180.242 Port 80

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Also, I’m getting the error message that state

Warning : DocumentRoot [/var/www/html] does not exist
apache2 could not reliably determine the server's fully qualified domain name using [IP Address] set the 'Server Name' directive globally to suppress this message.
Virtual Host Configuration *:80
(Domain Name) (etc/apache2/sites-enabled-000-default.conf:4