By default, an SSL certificate will be installed automaticallly within a few hours of pointing your domain to Hostinger cPanel nameservers:

If you need to perform a manual installation, navigate to the Security section and click on SSL/TLS Status:

Select the desired domain or subdomain from the list and look for the AutoSSL button. If the button appears as AutoSSL is in progress..., wait a few hours for the process to complete. Otherwise, click on it to start the installation:

That's it, now your website will be protected with AutoSSL 🔒