How to create webservice interface between 2 systems

Hello i want to create a webservice interface between 2 systems using login request response technique in php. I am very much new in webservices systems and trying to learn the basic things first. I would like to know what are the basic things i have to learn in order to create interface between such systems. I have small project under which i want to create webservice interface between 2 systems in order to fetch valuable information from database. I have instruct an example in order to create such systems: Does anyone have an idea or any suggestions in order to create such interface ?

Login request to look like this. 
<LoginRequest> 
<user> user </ user> 
<password> pass </ password> 
<corporate_group_id> 101 </ corporate_group_id> 
<dealer_number> 11111 </ dealer_number> 
<dms_id> 12345678 </ dms_id> 
</ Login Request> 

The answer for success looks like 
<LoginResponse> 
<token> uiih37 </ token> 
<login_id> 8487292 </ login_id> 
<status> 
<success> true </ success> 
<code> 0 </ code> 
<message/> 
<browserURL/> 
</ status> 
</ Login Response> 

In response, we get a URL on success. 
<ns1:addRepairCalculationResponse> 
<status> 
<success> true </ success> 
<code> 0 </ code> 
<message/> 
<browserURL>http://ift.tt/1sdHLa6; 
</ status> 
</ ns1: addRepairCalculationResponse> 
This URL must be started in the browser. 
In your browser, the vehicle will then be processed and a calculation can be performed. 
When the calculation is complete in the browser, the browser can be closed. 
pick up car 
<getRepairCalculationRequest> 
<token> uiih37212p54h7mk8789203oh3bahq4l </ token> 
<login_id> 8487292 </ login_id> 
</ getRepairCalculationRequest>