The post gives a basic Idea about the web services inbuilt with the SharePoint which can be used in other types of desktop application and Silverlight application.

The SOAP request has to be sent in the web request body to get the response from the web service.

eg: SOAP call for getting the WebCollection.

"<?xml version=""1.0"" encoding=""utf-8""?> 
<soap12:Envelope xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:xsd=""http://www.w3.org/2001/XMLSchema"" xmlns:soap12=""http://www.w3.org/2003/05/soap-envelope""> 
    <soap12:Body><GetWebCollection             xmlns=""http://schemas.microsoft.com/sharepoint/soap/"" /> 
     </soap12:Body> 
</soap12:Envelope>";

The most commonly required url’s for interrogating with the SharePoint web. Replace the localhost with your SharePoint server url and hit the enter and you will see the SOAP request and reply format.

• http://localhost/_vti_bin/Webs.asmx - sites and sub sites
• http://localhost/_vti_bin/Lists.asmx - Lists
• http://localhost/_vti_bin/Alerts.asmx - Alerts
• http://localhost/_vti_bin/DspSts.asmx -Schemas and data
• http://localhost/_vti_bin/DWS.asmx - Document Workspaces
• http://localhost/_vti_bin/Forms.asmx –User interface forms
• http://localhost/_vti_bin/Imaging.asmx - Picture libraries
• http://localhost/_vti_bin/Meetings.asmx - Meeting Workspaces
• http://localhost/_vti_bin/Permissions.asmx - SharePoint Services security
• http://localhost/_vti_bin/SiteData.asmx - SharePoint Portal Server
• http://localhost/_vti_bin/Sites.asmx - Site templates
• http://localhost/_vti_bin/UserGroup.asmx - Users and groups
• http://localhost/_vti_bin/versions.asmx - File versions
• http://localhost/_vti_bin/Views.asmx -  views of lists
• http://localhost/_vti_bin/WebPartPages.asmx - Web Parts

Hope this gives a basic idea about web services and the further post will explain in making a web service call..