Guides and Margins.
I assume you're talking about one of these sheets (probably from Ryman office supplies) with a pre-formatted layout of business cards so that you can tear them apart. My novice advice would be not to use these, as they are a bit thin and the perforated edges do not look clean. Obviously you can cut them with a steel ruler and very sharp blade. Anyway if you've spent money on them and want to use up to you buddy.
Photoshop is not ideal program for layout but it will do the job. You want to open a new file (presumably a4 size), go to 'view' select 'rulers', now you should see rulers on the sides. Now you might be unlucky and have inches or something like that, I would suggest changing these to mm as building sites use mm to be more accurate so on a little sheet of paper you should be using mm or maybe even pixels but I don't really relate to pixels so lets do mm.
Go to top left of your menu bar where you see 'photoshop' click on it, menu comes down go to 'preferences' across or click to 'units and rulers' and click. Select mm, there's all different settings you can change, have a look through these and see if there's anything else you'd like to change.
Now your rulers measurements should change.
On your pre-formatted sheet measure where the lines are coming from (from the top-left corner or wherever you fancy).
Now go to the top left inbetween the two rulers (a little square) see picture, drag this to the top left corner (or wherever you measured from) what this is doing is setting where the rulers measure from. Now you click on the ruler and hold down, drag along and you'll see a guide coming along. Set it where you want your margins, when you let go it will place. I suggest zooming in when doing this; it will give you greater accuracy. Set all your guides, Now you should see a layout that is the same as your pre-formatted sheet you have in your hand.
Open the file of your single business card, you want to select everything (on every layer and every item) becareful not to move them, you might want to flatten the layer, if you do make sure you save as a different name to keep your original. I would suggest doing this anyway even if not. Go to 'edit' hit 'copy'. Now go to your other document with everything layout, hit 'paste' you should now see your card. Move it and lay it out, Hit 'paste' again and you should see another card, move it around.
Now I'm not sure if this is the best way in the world as when I did it I could never get them perfect on the pre-formatted card, not sure if printer was loosing accuracy, I don't think you can enter the actual set out numbers numerically in photoshop, if you can do this as it will ensure greater accuracy. Hopefully a real pro will improve on what I've said.
Good luck, let us know if you run into any problems.
