The following steps are actually simple if followed in the right way...
Here we will be trying to get the below picture from three others
Step1
Get the first photo of the dog(1).
Step2
Get the second photo of the dog(2).
Step3
Now got the background photo where all main characters would be placed.
Step4
Select the main character with wound tools and past it on the background (dog1).
Step5
Repeat the same prosses for dog2.
Note that the second dog is way back so you have to blur it a little bit and make sure its not too much.