There are a number of ways of making a grid board using Adobe Photoshop, and almost as many tutorials as methods. Ultimately, all of them return to the idea that you need to create a square object to help you make a grid pattern. There are just a wide number of ways of getting started. I have posted these links in their order of usefulness. You'll have to decide on the method that works best for you.
One word of advice: start by imagining how big you want the board and then calculating how big you want each square. It will speed things up considerably and prevent you from having to do it over. As carpenters always say: measure twice, cut once.
Creating a Grid with a Custom Pattern in Photoshop
I liked this tutorial best, not only because it is in video form (which is easier than reading) but because I think the method it shows is probably the quickest and most effective and teaches you some interesting Photoshop skills -- especially in the use of strokes. It also shows you one way of decorating the squares.
This tutorial is focused on using a grid as a background for a header graphic (which might be useful to know for your box design), but the method it offers for making the grid is very simple.
How to Create a Grid Quickly and Effectively in Photoshop
This one also offers a rather painless method in very few words. It also shows you how you can use a picture as the background of your board.
Making Grid Masks in Photoshop
This might be a good method if you want to use a picture as the background.
Photoshop Tutorials - Custom Grid
This is the method I discovered on my own for making a grid and it works -- but it is not as cool or simple as the ones above.
I threw this one in just in case someone likes the idea.
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