i created this simple app.

doc.Load(this.TextBox1.Text);

The += operator is the same as saying "Label2.Text = Label2.Text + title;"

It adds the next title on every pass.  If you only use the = operator, your Label2.Text is completely cleared and reassigned every time.

Hope this helps!

-figz 

Label2.Text +=title  :  Label2.Text = Label2.Text  + title

When you say "label.Text = whatever" in each iteration of the loop, you are overwriting the previous value of the label.

When you say "label.Text += whatever" it is the same as saying "label.Text = label.Text + whatever".  this means it is concatenating "whatever" to the previous value of the label.