Syntax error in INSERT INTO statement. System.Data.OleDb.OleDbErrorCollection

Your code is correct, apart from the lacking of using statement around disposable objects, but the real problem is the word NUMBER. It is a reserved keyword for MSAccess.
Use it enclosed in square brackets.

string text = "INSERT INTO TEST ([Number], Amount) VALUES (?, ?)";

However, if it is still possible, I really suggest you to change that column name. This problem will become very annoying.

protected void Button1_Click(object sender, EventArgs e)
{
    string conString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\admin\Desktop\del\SHAFI\db.accdb";
    using(OleDbConnection con = new OleDbConnection(conString))
    using(OleDbCommand cmd = con.CreateCommand())
    {
        string text = "INSERT INTO TEST ([Number], Amount) VALUES (?, ?)";
        cmd.CommandText = text;
        try
        {
            con.Open();
            cmd.Parameters.AddWithValue("@Number", txtAmount.Text);
            cmd.Parameters.AddWithValue("@Amount", txtOrder.Text);
            cmd.ExecuteNonQuery();
        }
        catch (OleDbException ex)
        {
            txtAmount.Text = "Sorry";
            Response.Write(ex.Message.ToString() + "<br />" + ex.Errors.GetType());
        }
    }

OleDbCommand does not support named parameters. You have to add the parameters in the order you want them.

//Code above
con.Open();
cmd.Parameters.Add(txtAmount.Text);
cmd.Parameters.Add(txtOrder.Text);
cmd.ExecuteNonQuery();
//Code below

You are using @Number and @Amount variables for Number and Amount but not writing these values in query.

? used in java not in asp.net(c#). so you are mixing these two.

protected void Button1_Click(object sender, EventArgs e)
{
    string conString = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Users\admin\Desktop\del\SHAFI\db.accdb";
    OleDbConnection con = new OleDbConnection(conString);
    OleDbCommand cmd = con.CreateCommand();
    string text = "INSERT INTO TEST (Number, Amount) VALUES (@Number, @Amount)";
    cmd.CommandText = text;
    try
    {
        con.Open();
        cmd.Parameters.AddWithValue("@Number", txtAmount.Text);
        cmd.Parameters.AddWithValue("@Amount", txtOrder.Text);
        cmd.ExecuteNonQuery();
    }
    catch (OleDbException ex)
    {
        txtAmount.Text = "Sorry";
        Response.Write(ex.Message.ToString() + "<br />" + ex.Errors.GetType());
    }
}

You should use:

string text = "INSERT INTO TEST (Number, Amount) VALUES (@Number, @Amount)";

instead of:

INSERT INTO TEST (Number, Amount) VALUES (?, ?)