with the elements that you give us, it is difficult to help you!
You could be talking about silkscreening, offset, lithography, etc...
I guess that you mean about offset/press priting, the more common.
4 colors is often quadrichromy: 4 plates are used: cyan , yellow, magenta, and black, to try to reproduce as accurately as possible the colors of your work.
There is way more info in your user guide about CYMK. different color profiles are used folowing the specificity of the press/paper/ink combo, so we can't give you an absolute answer.
But it is possible to have a job with 4 spot colors: for instance: black, gold, a glossy finish, and a pantone color... it is really different.
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For the two colors, it could be a duotone: two colors are used to create more tones., or it could be black plus another color, that is just used to create some titles, etc...
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For the resolution, the rule of thumb is to use 1.5x the LPI used for printing.
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Usually, printers do not like native photoshop files, they prefer PDF, or files produced in a DTP app, like In design /quark Xpress/pagemaker.
You'll need to join the fonts with the file so that the RIP (raster image processor, the device used to produce the films that will be used to create the printing plates)wil be a ble to process the file.
Make sure that their license allow for redistribution!
In some places, the validity of the license of your design program is checked :
see here
The best person to ask for the specifications of your file is the printer itself!
2 Color Printing and 4 Color Printing 
Linear Mode
