Samples are a great way to see if you really want to invest your hard earned $$'s in a new book. A sample is just that, a sample, and you can get samples of any book you see the send sample now button. I want to say samples are available for all the Kindle books, but I can't for certain. I can say I haven't seen one yet that didn't have the send sample now button as an option.
If you have multiple Kindle devices (Kindles or iPhone, iPad, Android, etc) there will be a Deliver to area with arrows to the right of the box so you can choose exactly where to send your sample. You will also see a link to a help section explaining How sampling works and another link letting you know you can get the sample on your PC or Mac too, depending on which you accessed the Amazon site with at the time.
Isn't it amazing how they know which computer you are using at any given time? Well, I am very comfortable knowing my information is safe with Amazon. I've been shopping with them for years with no problems at all... And they didn't pay me to say that.
If you do decide to try a sample or two (or three or four), remember you are never under any obligation to purchase the book. When you are finished with the sample, if you have purchased the book or not, delete it by right clicking on it (using the 5 way right button) from the Home screen. Then choose Delete, confirm that is what you really want to do, and be done with it.