Creating A Matte Painting in Photoshop

Firstly what I did was obviously open Photoshop and I also downloaded the photos the person used in the tutorial I watched, to try and replicate exactly what he did and hopefully to end up with the same result. The pictures I downloaded were: The side of a mountain with water next to it, a boat, an ocean and a foggy city.

Firstly, when I opened Photoshop, I created a new background and opened up the picture of the mountain and resized itand moved it to the left so that part of the image went over the background area, leaving some white space next to the image, I then renamed the layer which contained the mountain image "Mountain". Next I opened up the picture of the ocean and scaled it so that it was in line with the water in the mountain image, I also moved the picture of the ocean more onto the left so that it partly overlaped the water in the mountain image. Like with the mountain layer, I named the layer "Ocean".

Then I "masked" the Ocean layer by pressing on the square with a hole in the middle.

Next, I selected the mask and used the Brush tool to erase part of the water that was overlapped. On the left where it shows you what colour is selected, I swapped the colours around, so white was my primary colour and black was my second. I did this to re-paint the water in case I erased too much water. So now the water from the Ocean layer was now slightly merged with the water in the Mountain layer and the water from the Ocean layer should also be in line with the Mountain layer water too.