Sharepoint CSOM Create a new SharePoint website

// Starting with ClientContext, the constructor requires a URL to the 
// server running SharePoint. 
ClientContext context = new ClientContext("http://SiteUrl"); 

WebCreationInformation creation = new WebCreationInformation(); 
creation.Url = "web1"; 
creation.Title = "Hello web1"; 
Web newWeb = context.Web.Webs.Add(creation); 

// Retrieve the new web information. 
context.Load(newWeb, w => w.Title); 
context.ExecuteQuery(); 

label1.Text = newWeb.Title;