Using Gradient to blend four images

[rich2005]

I do not think there is a newby terms explanation. You can always fix-up first two layers with layer mask, make a layer from visible Layer -> New from visible  combining the two and then continue with layer 3 (and mask). Repeat the process and add layer 4 and mask.

or depending on the images I might try using layer groups as this.

   

From Gimp 2.10 a layer group can use a layer mask