you can use this.
privte void on Form1_load(Object sender , EventArgs e)
{
DataSet ds = new DataSet();
string str = "select * from user1 ";
adap = new SqlDataAdapter(str, con);
adap.Fill(ds, "user1");
dataGridView1.AutoGenerateColumns = false;
dataGridView1.DataSource = ds.Tables["user1"];
dataGridView1.Columns["FirstName"].DataPropertyName = "FirstName";
dataGridView1.Columns["LastName"].DataPropertyName = "LastName";
dataGridView1.Columns["username"].DataPropertyName = "username";
dataGridView1.Columns["password"].DataPropertyName = "password";
}