Design your artwork/layout on top of the template, and then print only the artwork/layout without the template. It doesn't really matter what orientation it is or where on the piece of paper the j-card is positioned -- unless you want to be economical like me and fit 2 j-cards on each piece of paper -- since you are going to cut it out, you just want to make sure that it entirely fits on the piece of paper and that the dimensions of the artwork/layout match the template's so it can be folded and fit properly in your norelco case. In Photoshop, the template would just be a layer that you could easily remove. I leave the cut lines at the edges to make it easier to cut the j-cards out.
This particular template is for a 4-panel j-card, with the extra flap. I love these and use these 4-panels myself, but you can also just do 3-panel j-cards if you want to make things a little simpler. If you're printing front and back make sure to rotate the reverse side artwork/layout 180 degrees from the front side and print both sides before cutting.
Lastly, I wouldn't recommend using letter paper, matte or light card stock or even luster/glossy photo paper works better. But that doesn't mean you can't use letter, and that some awesome DIY artists haven't used it before.
Last Edit: Nov 28, 2022 12:58:24 GMT -5 by engraven
You'll need your artwork layout to be perfectly overlaid on the template, with your front artwork precisely where the front is labeled on the template, your spine precisely where the spine is labeled, etc. The dimensions need to perfectly match, or it won't fit in the norelco properly.
By "make sure that it entirely fits on the piece of paper" I just meant that it doesn't necessarily matter if it is perfectly aligned in the center of the page or anything, just so long as none of it is cut off at the edge of the paper.