how to use sql server database from server system to client

Question

Hi,

 Please Help me..... In my  c# project i want to use one database from  server computer and want to run my application on all other client PC connected to this network to use the same database. I installed sql server 2012 in my sever computer and change the TCP/IP property enable.Now i try to use my database from another PC  but i faced the error "a network related or instance specific error occurred sql server 2012. The Server was not found or not accessible. Verify the instance name and configure to allow remote connection."My connection string was 

          public static string str = " Data Source = WIN-6A67QTTNU6J\\SQLEXPRESS;Database = Sample;Integrated Security = True";

 

 

 I refer all related link and do the steps but still  no solutions...Please help... Last 10 days i am searching this i am new in c#.. 

 It is possible or not... Or I want to install sql server in my client machine to configure it. Plese answer me in detail....

Waiting eagerly for answer 

Thanks for everyone in advance