The clients printer asks for "5mm bleed with no guide/crop/reg marks" I am slightly confused by this? what does it mean? Does it mean I just have have photoshop guides? or does it mean I have no guides at all and keep that space empty?
I think you should ask the printer.. but it would appear that your document is to have a 5mm bleed with no guides, crop marks, or registration marks on output.
I would really advise instead of using Photoshop you use InDesign for a print document.
InDesign -> New Document or shortcut cmd+N
Enter print measurement in width and height:
Expand Bleed and Slug:
Enter in Bleed measurements:
Document setup example of corner:
I recommend InDesign because the last I recall to setup a bleed in Photoshop was a daunting manual process, but in reality Photoshop used for print is typically frowned upon. I would ask your client to give you the contact number for the printer to converse and I really wouldnt play the middle man game with designer to client to printer.
If you do a Google search there are several tutorials on this topic.
It is better to do that in Indesign. In photoshop u can do a virtual bleed, add guides to the document margin (just for reference) then add 5mm more to the document canvas size (10mm to the document width and 10 to height).
To add to the answers above, which are all quite informative... you should use InDesign, as mentioned, and create a document with 5mm bleed on all sides as Matt said. You'll also have to make sure your original .psd has additional bleed (as Scott said). Then you can import that .psd file into your InDesign document. Make sure the image extends to the red line around the document border, as in the last image Matt posted.
The important part that I think hasn't been mentioned is that you should then Export a PDF from InDesign, to provide to the printer. Typically printers prefer a PDF over native InDesign files, so there are no issues with missing images, missing fonts, etc.
When you export a PDF from InDesign, you can select "Marks and Bleeds" from the side menu in the dialog box that opens up (after naming the PDF file). In the "Marks and Bleeds" section, you can set the Bleed to "Use Document Settings" (which you already had set to 5mm when you created the new document, and make sure all of the boxes under and including "All Printer's Marks" are UNchecked (they may be unchecked by default).
These settings will give you a PDF with the correct amount of bleed, and with no printer's marks, as requested.
In Photoshop you would simply make the nonprinting guides for you to use as a visual guide and make the canvas size 5mm larger on each side. Since you are working on a file that will be printed, the best program to use at this stage would be InDesign. When creating a new document, add a bleed of 5mm to each side. Then, import the psd into InDesign at original size and you should be good to go. When you export as a pdf or print it directly, simply make sure that the under marks and bleeds, the checkbox for All Printer's Marks is unchecked and the checkbox that says Use Document Bleed Settings is checked.
In Photoshop, just make your file 10mm wider and 10mm taller and ensure all content extends to the document edge.
Realize that 5mm on each side will be cut off. So, don't place anything important in that 5mm.