on apex.oracle.com, a wallet has been installed by Oracle operations. On your local system, you need to take care about that yourself.
This article gives some guidance:
From your provided link i do not understand below line
Next, use your browser to navigate to the HTTPS URL you are about to access with APEX_WEB_SERVICE or UTL_HTTP (in this example, we use Firefox).
It says you have to install certificate for the website you are about to access but how does apex.oracle knows all the websites certificate i am about to call?
Is it that you just have to install any certificate
please have another read of the web article. You don’t have to install a certificate for each web site which is to be accessed from APEX. Instead, the root certificates are required. The article describes how to get the root certificate for one example website. That will be valid for other web sites as well. So you would need to assess which websites are to be accessed and then to add the root certificates for all of them - probably you‘ll need less root certificates than web sites.
For apex.oracle.com, about 50 to 60 of the most common root certificates have been added to the wallet - that‘s why most websites work out of the box on apex.oracle.com. Unfortunately this wallet is not available for download.
if you have a java keystone with root certificates available, you can convert that to a wallet as follows.
Thank you for the clarification , it will be very good if oracle can provide the wallet or certificates being used by apex.oracle.com though