I think you'll enjoy working with AI Gigapixel (AIG) and discovering what it can do for you! Both for individual photos and batches of photos....
After you launch AI Gigapixel, look on the right side of the interface. Down towards the bottom there's a section called "Output". I'll attach a couple snips so you can see two different ways of approaching where to save... (1) You can either have your AIG image(s) stored back into the same image folder where your original images are located (see my snip with that box checked on), or (2) You can uncheck that box (yep, another snip attached!) to browse your computer and decide where you want the AIG output to go.
A handy tip I use to make it easier to spot the AIG output files is this: if you look down to the option in that Output box that says "File Suffix" .... After the word "output" in the grey box to the right of those words I add a hyphen. Following that hyphen I enter the amount of upsizing I used in AIG. For instance, if I upsize 400%, I'll doctor that entry to read ....-output-400 . That way when I scan down my list of image filenames it's easier to spot the ones I enlarged with AIG. And, if you want to try different scaling options for a single image then you know which is which. Neat, hunh?
Topaz runs some excellent webinars for free. You may want to get on their mailing list to be notified when they're being held, so you can register. In the meantime, you can also look at their online archive of past webinars to get some tips from talented experts re: how to use tools like AIG (AI Gigapixel) and the other Topaz filters, plugins and Studio tools.
Check out: http://blog.topazlabs.com/webinars/
Good luck! Have fun playing around with AIG and the other Topaz Studio adjustments..