Why we Use Certificates In WCF - wcf

Question

I am working on University Management System on which i am making WCF service....
my requirement is to Secure my web service (WCF) over the internet for this someone told me use certificates but i do not know how to use certificates
i have also implemented Https protocol and i am using WshttpBinding
This is My Web.config file :-
<?xml version="1.0"?>
<configuration>
<system.diagnostics>
<sources>
<source name="System.ServiceModel.MessageLogging" switchValue="Warning,ActivityTracing">
<listeners>
<add type="System.Diagnostics.DefaultTraceListener" name="Default">
<filter type="" />
</add>
<add name="ServiceModelMessageLoggingListener">
<filter type="" />
</add>
</listeners>
</source>
<source propagateActivity="true" name="System.ServiceModel" switchValue="Warning,ActivityTracing">
<listeners>
<add type="System.Diagnostics.DefaultTraceListener" name="Default">
<filter type="" />
</add>
<add name="ServiceModelTraceListener">
<filter type="" />
</add>
</listeners>
</source>
</sources>
<sharedListeners>
<add initializeData="d:\khurram\projectalahsaan2014\alahsaan\dal\web_messages.svclog"
type="System.Diagnostics.XmlWriterTraceListener, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
name="ServiceModelMessageLoggingListener" traceOutputOptions="Timestamp">
<filter type="" />
</add>
<add initializeData="d:\khurram\projectalahsaan2014\alahsaan\dal\web_tracelog.svclog"
type="System.Diagnostics.XmlWriterTraceListener, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
name="ServiceModelTraceListener" traceOutputOptions="Timestamp">
<filter type="" />
</add>
</sharedListeners>
<trace autoflush="true" />
</system.diagnostics>
<connectionStrings>
<add name="DAL.Properties.Settings.ConStr" connectionString="Data Source=.\SQL2012;Initial Catalog=AlAhsaan2014;Integrated Security=True" providerName="System.Data.SqlClient" />
</connectionStrings>
<system.web>
<compilation debug="true" targetFramework="4.0" />
<!--<httpRuntime maxRequestLength="2147483647" executionTimeout="3600" enable="true" />-->
<!--2147483647-->
<sessionState mode="InProc" cookieless="true" timeout="20"> </sessionState>
</system.web>
<system.serviceModel>
<diagnostics>
<messageLogging logEntireMessage="true"
logMalformedMessages="true"
logMessagesAtTransportLevel="true" />
</diagnostics>
<bindings>
<wsHttpBinding>
<binding name="secureWsHttpBinding"
maxBufferPoolSize="2147483647"
maxReceivedMessageSize="524288000"
messageEncoding="Mtom"> <!--500MB Download-->
<readerQuotas maxArrayLength="1572864"/> <!--1.5MB Upload-->
<security mode="Transport">
<transport clientCredentialType="None"/>
</security>
</binding>
</wsHttpBinding>
</bindings>
<protocolMapping>
<remove scheme="https"/>
<add scheme="https" binding="wsHttpBinding" bindingConfiguration="secureWsHttpBinding"/>
</protocolMapping>
<behaviors>
<serviceBehaviors>
<behavior>
<!-- To avoid disclosing metadata information, set the value below to false and remove the metadata endpoint above before deployment -->
<serviceMetadata httpsGetEnabled="true"/>
<!-- To receive exception details in faults for debugging purposes, set the value below to true. Set to false before deployment to avoid disclosing exception information -->
<serviceDebug includeExceptionDetailInFaults="true"/>
</behavior>
</serviceBehaviors>
</behaviors>
<services>
<service name="DAL.AlahsaanDSL">
<endpoint address="" binding="wsHttpBinding" bindingConfiguration="secureWsHttpBinding"
contract="DAL.IAlahsaanDSL" />
<endpoint address="mex" binding="mexHttpsBinding" contract="IMetadataExchange" />
</service>
</services>
<serviceHostingEnvironment multipleSiteBindingsEnabled="true" />
</system.serviceModel>
<system.webServer>
<modules runAllManagedModulesForAllRequests="true"/>
</system.webServer>
</configuration>
My Question is :-
What are the mechanism of Certificates?
How to Use Certificates?
Does Certificate provide (PKI) (public key infrastructure)?