Here’s a quick guide on exporting a board from Altium Designer 14 to be made by OSHPark.

1. Go to Design -> Layer Stack Manager
2. Set your stackup to be this:

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This information was derived from this FAQ.
3. Go to Project -> Compile PCB Project.  Fix any errors that could cause a problem.
4. Go to File -> Fabrication Outputs -> Gerber Files
5. Under ‘General’, set the units to be ‘Inches’ and the Format to be ‘2:4’
6. Under ‘Layers’, select the following layers:

• Top Overlay
• Top Paste
• Top Solder
• Top Layer
• Bottom Layer
• Bottom Solder
• Bottom Paste
• Bottom Overlay
• Mechanical 15(assuming that you have drawn your board outline on mechanical 15)

Now export, save as <projectname>.cam

7. Go to File -> Fabrication Outputs -> NC Drill.  Use the following settings:

• Units: Inches
• Format: 2:4
• Leading/Trailing Zeros: Suprress trailing zeros
• Coordinate Positions: Reference to relative origin
• Other: Optimize change location commands

Save as <projectname>-NCDRILL.cam

8. With the NCDRILL.cam file selected, go to File->Export->SaveDrill.  Set the extension to be .xln

9. Go to your project folder, there should now be a sub-folder called ‘Project Outputs for <Project Name>’.  Grab the following files:

• *.xln
• *.GBL
• *.GBO
• *.GBP
• *.GBS
• *.GKO(re-name the .GM15 file to be .GKO)
• *.GTL
• *.GTO
• *.GTP
• *.GTS

Put these all into a .zip folder.

10. Upload the .zip folder to OSH Park.

11. Have fun!