\\How can you tell if you have a 1st edition?;

For US editions it will be clearly marked on the copyright page, which is on the back of the title page.

This is the copyright page.

All we're going to pay attention to is the little line of numbers usually at the bottom of the page. The last number (which will be the lowest) is the number of the printing.

As you can see it's a first edition. Here's another book I have that's not first edition just for an example.

The lowest number is 4, so it's 4th edition.