LDAP

Question

Hi All,
I am new to MVC Website development.  When I debug my website and try to login in my website I get this exception "Unable to establish secure connection with the server"  @(Membership.ValidateUser(model.UserName, model.Password) in the code. When I saw the web.config file they have specified a LDAP connectionString with an IP address.  Can someone please tell me about the usage of LDAP , how I can establish a LDAP server on my machine and how it helps in providing membership or roles. I am using SQL Server 2008, Visual Studio 2010.
I am completely unaware of the LDAP concept. 

Thank you in advance.