The first is a simple typo and should be, as you say, TextBox2.Text.
The second is more interesting and shows a) a major difference between VB
and C#, and b) I didn't check the code (more on that later). The line should be:
Label1.Text = (Convert.ToInt32(TextBox1.Text) + Convert.ToInt32(TextBox2.Text)).ToString();
This adds the two numbers together and then converts them back into a string to display.
The error here is completely mine and is interesting. In VB
you don't need to convert the two numbers back to a string - it is implicitly done for you. When I converted this chapter from VB
I completely forgot this and didn't try the code becuase it wasn't going to be part of the code that finally shipped. An oversight and I should have been more careful; I can only apologise.