A Gold Metallic colour is a special ink that is required. It is specially made and it requires it to be a spot colour.
You basically have 3 colour models (not including LAB to keep it simple)
For screen you have RGB
For Print you have CMYK and Spot
RGB is perfect for screen, looking at things on monitors and websites.
For print you need to have CMYK - Cyan Magenta Yellow and Black (K is used probably because B is used in RGB - Red Green Blue)
So C M Y are secondary colours. They mix to form R G B. When you print C M Y they are in tiny dots, your eye isn't sensitive enough to separate the colours as the RGB light is reflected off the paper (RGB light comes from the sun and any other direct or reflective source, like paper or grass). So they blend nicely into RGB which our eyes can interpret.
Where does K come in?
Well because of impurities in the Ink, mixing CMY doesn't give a solid black, it gives a muddy grey-green colour, so a black pigment is used instead to reproduce Black colour.
Spot colours are colours that can't be reproduced by CMYK. They are special colours that fall outside the GAMUT (range of colours that CMYK can possibly make). They are mainly used for specific branding, logos with up to 3 colours only etc.
Some logos, branding, printed material etc. require to have a very specific colour, so sometimes you would need to print CMYK and 1 spot colour or 2 spot colours.
You wouldn't want to print a print job with 8 spot colours, that would mean it's double the amount of plates needed (CMYK) to reproduce the colour, therefore doubling the cost, effectively.
So for most print jobs people print using CMYK. Even if a spot colour is used in a logo, they convert the spot to CMYK to save money on an extra plate.
When a printer receives the file, they can separate the CMYK, these are the separations. They are each printed onto a plate for printing (it's a thin metal plate with emulssion that is burned away by a laser to form the shape of whatever your printing, from letters, to illustrations to photos) this is know as the the RIP stage (Raster Image Processing).
What you're looking for is to create a document/logo or whatever you're doing, so that it is printed with a special spot colour, called a metallic ink. Which is exactly what it is. It's an ink with metallic properties, specially made and it gives a shine off it just like metal would.
This is a spot colour, it's a special ink that has to be made or bought in.
PANTONE SOLID 873C (or 873U) is the colour you're looking for. It is found under Window>Swatch Libraries Pantone Solid Coated or (Pantone Solid Uncoated. The difference between C (coated) and U (uncoated) is that this refers to the type of paper you're printing on, as the inks are mixed with different, let's say saturations, for different stocks of paper.
This Pantone Coated or Uncoated colour will appear as a separate plate at the RIP stage and will contain only the artwork that is coloured with this spot colour in illustrator/photoshop/indesign/quark or whatever program you're using.
You can drag this swatch from the Pantone Solid Coated/Uncoated window and into the swatches panel of Illustrator.
You can tell if a colour is a Spot colour by a white triangle with a dot in the lower right colour of the swatch.
The rest of your illustration should be used with CMYK inks.
Any photos embeded or placed in illustrator should be CMYK.
You should also hand over all the artwork, including Illustrator file, any linked or embedded images, any fonts used to the printers.
You should also give them detailed printouts of your artwork, detailed instructions of what you want done. If you can, you should visit your printers with the files and sit down with a designer and they can help you sort it out to have it perfect for print.
