The big box that you see IS the uploader.
After the uploader box opens, go to the bottom of the box, to the right of the blue buttons, where it says FOLDER.
Use the drop-down box to select the folder where you want your images to go. If you haven't created a folder yet, you can do that from the FOLDERS link at the top of the page and then come back to the uploader. I name my folders as the name of what I'm selling - for example, if I'm selling a stuffed alligator, I'll name the folder Alligator.
After you've selected the folder you want the images to go to, then click in the uploader box.
Then go to your images on your computer (I do it from Windows Explorer, where I can see everything clearly), and drag and drop the image(s) to inside the box. You should see the path name of the image(s) inside the box. If you don't, click inside the box and try it again.
Once you see the name of your image(s) in the box, click the blue UPLOAD button at the bottom of the Uploader screen. You will then see a progress bar as the pics upload.
When the upload process is completely done, you will see a confirmation message.
Good luck!
2purrcats