How to place inside an object
This example will help to place an object inside. It is very funny example because I am going to place a gentleman in the car.
Car Picture: Take a car picture to modify.
Gentleman: Take a gentleman picture as here.
Selection: Choose Polygonal lasso tool (L key) and make selection to place gentleman.
Selection: Make selection by the Polygonal lasso tool (L key).
Paste: Go to Edit menu > Click Paste Into (Ctrl +Shift + V).
Now change the layer settings as here.
This is your final result.