how to insert data into a table in database using textbox

That's a very general question, but...because if you get it wrong you open yourself up to SQL Injection, which can damage or destroy your database, I'll answer it:

using (SqlConnection con = new SqlConnection(strConnect))
    {
    con.Open();
    using (SqlCommand com = new SqlCommand("INSERT INTO myTable (myColumnName) VALUES (@MYDATA)", con))
        {
        com.Parameters.AddWithValue("@MYDATA", myTextBox.Text);
        com.ExecuteNonQuery();
        }
    }