Hey can anyone tell me how to install SSL certificate on my Digital ocean VPS server?

Please its urgent

I have the domain of this VPS server hosted on hostinger.com

You can use certbot/letsencrypt

can you send me a document, because its not happening. I tried using certbot, but its showing apache error

You should Google 😉

Certbot is very easy to use. If you don't have full control on the server than you should generate your own cert files.