OK, let's start from the beginning. For this example, I'm only going to show you how to clip and image to shape.
Let's create the shape first. (Don't worry about the document size for the moment)
Select you Rectangle Tool.
Set the tool to shape. Set the tools fill color to black. Turn off the stroke.
Click once in the center of your document and to open the 'Create Rectangle' UI.
Enter your height and width parameters. (2.0in x 2.3125in)
This will create a 2 x 25/8 in black rectangle in the center of your document.
Now, let's make this photo of this cat be constrained to the black rectangle.
First you need to select/highlight the Cat's layer.
Second, you need to right click the Cat's layer and choose, 'Create clipping mask'.
You will now have something like this.....
Make sure you select/highlight the Cat's layer.
In order to size the image, you will need to enter Free Transform (Cmd/Cntrl + T)
Hold the shift key and the alt/option key to constrain the photos proportions.
Mouseover one of the corner handles, click and drag to re-size the image to fit in the cell the way you like.
Hit enter or the checkmark to accept the state changes.
Here is what the layers panel should look like....
This is how you create a specifically sized rectangle and clip and image to it.
There is no drag and drop method with Photoshop, you will have to resize each image you add to the cells.
Next I will show how to make the template.