Let's get started.

1. Open Photoshop.

2. Create a new document.
>File
>New
Create a 4 inch by 6 inch, White Background document. Name it Coat Of Arms.

3. Set up rulers and guides.

(An aside: We created a 4 inch by 6 inch document. What is the middle? Where is the middle?)

From the top menu select.
> View
>Rulers
and ruler marks should appear. The next step is tricky. We need to set guides for the middle of the document. Move the cursor to the edge of the document where the ruler marks are and press down on the mouse button. Then drag the guide to the middle of the document. What is the middle? Do this to both the horizontal and vertical.
Below is how your document should look.