1. Click on Load. There you have two choices. You can key in the URL of a website or simply choose your own words. Click submit, then move on to the other things you can do with those words.
Here's the results using this blog's address.
2. If you click the circle with the arrow (next to Color, Theme, Font...), the app gives you random choices. If you click on the arrow to the right of your choices (don't forget the Shape choice a bit lower on the page), then you can make specific choices rather than the random ones.
3. You can even click on History and see all the changes you've made (and return to an earlier choice, I think. I didn't actually try to do that).
Here's where I started (what was on the screen when I opened the app until I figured out what I was doing)
The final product
The app allows you to share your results with various social media, but I just used the snipping tool to save these (later I realized that I could actually save the image in various forms, including as a JPEG or PNG). I didn't completely explore the app, but I could see that it might have its uses (beyond simply goofing around with it as I was doing). It might be useful in making a scrapbook image, for example, for creating a repeating image or for a website.
Note: Later I found this document titled 101 Ways to Use Tagxedo. There's also a gallery with some very cool images (Harry Potter, for instance), and a FAQ page.I haven't fully explored the Tagxedo app yet, but I can see that it might prove useful at some point.
Note: You may need Silverlight (which I installed on my computer a long time ago). Not quite sure about that.