Seasons

Open the starting file "Seasons" from your Z:>GA8 folder. 

All the layers should be hidden except the fall and winter one. Click on the "fall" layer.

Add Mask to the fall layer. 

Select the Gradient tool.

Drag it from very close to the edge of the top photo onto a bit of the photo below so the edges blend together.

Repeat for the Summer photo: add a mask to that layer, drag the Gradient tool from the bottom of the summer photo up a bit.

For the Spring photo, was want to have it blending in two directions. In order to do that, click on the mask for "summer" (should be highlighted in yellow)...

Select the Gradient tool, and then go to the Properties panel. Change the blend mode to "Darken".

Then drag the Gradient tool from the left edge of the photo to the right. .

Add a mask to the "spring" layer, and using the Gradient tool, blend from the right inward and from the bottom up. Your layers will look like this...

and your photos should have something like this...