How do you put a grid on a layout in Photoshop?

Question

PSD

Good afternoon! Such a question - I want to try to typeset using a grid. I chose the layout, the width of the main part is 960px. I began to look for a psd layer (sorry if I didn’t call it correctly) with a grid. And there seems to be enough of them, but it turns out that they are 940px wide and plus 10px on each side. So these indents will climb onto the layout. So the layout should be 940px? I understand that the edges of the columns should go exactly with the image? Is it a curved layout or there are meshes without these side paddings.
PS I understand that in Photoshop you can draw a grid, but if you remove these indents, then the width of the columns is not divided by the number??? Maybe someone will tell you, sensible material on this case, otherwise there is a lot of information, but everything is the same.

Answer 1

That's not how it's done. If you already have content, build your grid around it. He should not now lie down on any substituted grid

Answer 2

Preview - new layout of the guide - there you can play as you like)