How to get start with SugarCRM REST API

Hello support.

I am currently working with an organisation which need to get data when an SugarCrm record is being created.

For this I try to use the REST API so we can get the records information and make a custom login on our end.

For this I see an example for exporting records via API on this link

As per that example we need the following information to proceed further:

$url = "http://{site_url}/service/v4_1/rest.php";
$username = "admin";
$password = "password";

I am trying to figure out from where I can get site_url? and which username and password is required to continue further.

Please provide a step by step tutorial or guide me to get the information for API use.

Thank you.