DataSource Controls :: Insert Into Entity Using Textbox And Button?

I am playing with trying getting the userid that is logged in and threadid from a querystring

and combine them with text that is being entered in a text box

and when the button is clicked that information would be inserted into an Entity Framework table

This is what I have so far. I'm a bit stuck on what to do on the button click.

protected void Page_Load(object sender, EventArgs e)
{
int threadID = Convert.ToInt32(Request.QueryString["Threadid"]);
int postId = Convert.ToInt32(Request.QueryString["Postid"]);
MembershipUser user = Membership.GetUser();
Guid userID = (Guid)user.ProviderUserKey;
var context = new MessageBoardEntities3();
// Load last post to textbox
var query = from p in context.Posts
where p.PostID == postId
select new { p.Post1 };
foreach (var result in query)
{
txtBxLastPost.Text = result.Post1;
txtBxLastPost.DataBind();
}
}
protected void btnPost_Click(object sender, EventArgs e)
{
//need code to insert
}