$ sudo apt-get install openssl          # Debian based systems 
$ sudo yum install mod_ssl openssl      # Redhat / CentOS systems 
$ sudo dnf install mod_ssl openssl      # Fedora 22+ systems

$ sudo mkdir -p /etc/pki/tls/certs
$ sudo cd /etc/pki/tls/certs

$ sudo openssl req -x509 -nodes -newkey rsa:2048 -keyout example.com.key -out example.com.crt

Generating a 2048 bit RSA private key
....................................+++
...................................+++
writing new private key to 'example.com.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [XX]: IN
State or Province Name (full name) []: Delhi
Locality Name (eg, city) [Default City]: Delhi
Organization Name (eg, company) [Default Company Ltd]: TecAdmin
Organizational Unit Name (eg, section) []: blog
Common Name (eg, your name or your server's hostname) []: www.example.com
Email Address []: admin@example.com

<VirtualHost _default_:443>
    ServerAdmin admin@example.com
    ServerName www.example.com
    ServerAlias example.com

    DocumentRoot /var/www/html

    SSLEngine on
    SSLCertificateFile /etc/pki/tls/certs/example.com.crt
    SSLCertificateKeyFile /etc/pki/tls/certs/example.com.key
</VirtualHost>

$ sudo systemctl restart apache2       # Debian based systems   
$ sudo systemctl restart httpd         # Redhat based systems

 https://www.example.com