Okay, so, as long as you've selected "Animation Wizard", the beginning is very easy and has the instructions already on the screen, so I'm just providing screencaps of that part and will have commentary on the rest.
For the canvas size, your images MUST all be the same size, otherwise the GIF will either A) look weird, or B) not work properly. I'm using 100*100 images, but, as an example, Carrie's GIF is 300*225.
I'm using images of Christian Kane for this example.
Okay, now comes the tricky part.
Click "Insert Blank Object" and drag the blank box to the bottom of the column. Make sure that the little blue eye is clicked next to the blank box.
Go to the bottom of the screen and click "Add Frame".
Click "Fill Tool" and then select a color in the forefront color box. Make sure it's the forefront, since otherwise it won't show up. You don't necessarily need these, but I think it looks cleaner. It's really just what you want, though, because it'll look fine either way
I used white, so this is what it looked like. The dotted line won't be there at the end.
This part's pretty optional, but it helped me keep track of where everything was. I duplicated the white frame and put one on either side of the images of Chris.
Now, select the first image and filler box. Right click and select "Tween". This is how you get the transition between images.
You can play with the settings, but make sure that your "start" and "end" frames are the right ones, otherwise it'll get messed up.
Your layout will look something like this:
Do the same with the other images. Then select everything between your start and end images.
Select "Duplicate frames". It'll automatically select the duplicates. Drag them onto the other side of the last frame.
Then click "Reverse frame order" and select "Reverse the order of selected frames".
That other white frame was just there to give me a visual for the end, and it's not necessary after the duplicates have been made, so if you have it there, you can go ahead and delete it.
Go to File, click Save As, select GIF, and save it
If everything went as planned, you should have a neat looking animation like this: