I am a complete newbie in terms of servers and unix systems. I have bought a domain, made a droplet and followed these 2 tutorials:
https://www.digitalocean.com/community/tutorials/initial-server-setup-with-ubuntu-16-04
https://www.digitalocean.com/community/tutorials/how-to-set-up-apache-virtual-hosts-on-ubuntu-16-04
I have also configured nameservers more than 24 hours ago & set up A records for both "domain" and "www.domain".

All possible tools say that my domain belongs to my droplet. However, the demo page is accessible only by droplet's IP address. I have tried seemingly everything.

domain.conf

<VirtualHost *:80>
    ServerAdmin mkeinviii@gmail.com
    ServerName domain.com
    ServerAlias www.domain.com
    DocumentRoot /var/www/domain.com/public_html
    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

apache2.conf

ServerRoot "/etc/apache2"
ServerName domain.com
Mutex file:${APACHE_LOCK_DIR} default
PidFile ${APACHE_PID_FILE}
Timeout 300
KeepAlive On
MaxKeepAliveRequests 100
KeepAliveTimeout 5
User ${APACHE_RUN_USER}
Group ${APACHE_RUN_GROUP}
HostnameLookups Off
ErrorLog ${APACHE_LOG_DIR}/error.log
LogLevel warn
IncludeOptional mods-enabled/*.load
IncludeOptional mods-enabled/*.conf
Include ports.conf
<Directory />
    Options FollowSymLinks
    AllowOverride None
    Require all denied
</Directory>
<Directory /usr/share>
    AllowOverride None
    Require all granted
</Directory>
<Directory /var/www/>
    Options Indexes FollowSymLinks
    AllowOverride None
    Require all granted
</Directory>
AccessFileName .htaccess
<FilesMatch "^\.ht">
    Require all denied
</FilesMatch>
LogFormat "%v:%p %h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" vhost_combined
LogFormat "%h %l %u %t \"%r\" %>s %O \"%{Referer}i\" \"%{User-Agent}i\"" combined
LogFormat "%h %l %u %t \"%r\" %>s %O" common
LogFormat "%{Referer}i -> %U" referer
LogFormat "%{User-agent}i" agent
IncludeOptional conf-enabled/*.conf
IncludeOptional sites-enabled/*.conf