Integrate Paypal into a SSL site

I would like to integrate Paypal Payment Gateway into my website, you need to add paypal button(this probably I will do it myself), insert invoice detail into MySQL(this probably I will do it myself too), process payment with paypal with my INVOICE_NUMBER, goback page to my website with [Payment Success, Thank you] or [Payment unssuccess], process ipn & pdt from paypal and insert the ipn &pdt details into MySQL. You need to do this in the actual environment instead of using sandbox, I will get somebody to test on your integration.

You need to install the ipn as per https://developer.paypal.com/api/nvp-soap/ipn/ht-ipn/.

I am using linux hosting, what I don't understand is this part in the above link:

// In wamp-like environments that do not come bundled with root authority certificates,
// please download 'cacert.pem' from "https://curl.haxx.se/docs/caextract.html" and set
// the directory path of the certificate as shown below:
// curl_setopt($ch, CURLOPT_CAINFO, dirname(__FILE__) . '/cacert.pem');
I already have the SSL certificate for my website, if the above required to install a new SSL, then you need to install the above SSL in a new subdomain.

You need to have many years of experiences in integrate Paypal Payment Gateway, please reply with message [I have many years of of experiences in integrate Paypal Payment Gateway] in your bid, and what you said should be a fact.