DMS is like a zip archive for disks.
WinUAE should support them natively, so you should be able to just mount it as if it were an .adf file.
On a real Amiga, you need to use DMS to unpack it to a floppy disk. If you have a way to get files onto your Amiga from your PC this can be simply downloaded from
http://aminet.net/package/util/arc/dms111