In order to enjoy DSDoom on your DS you will need a device which allows you to run unsigned code. When we first started creating homebrew applications this was acheived using a standard GBA flashcart and a device called a PassMe which bypassed the check for official code. Later we gained access to devices which allowed you to run code from adapters using compact flash and SD cards and these are now the recommended method for most users. These are known as media devices.
When we created DS Doom there were many media devices currently on the market which run DSDoom with varying degrees of success. These days pretty much any device you can buy should be able to run DS Doom with no trouble. We did have some recommendations on this page but sadly these are no longer stocked by Electrobee. Right now we're looking for an affilate relationship with another supplier and we'll update our recommendations when we can.
Disclaimer: If you have a media device that has a suitable libfat DLDI driver, you will be fine. Therefore, if you have trouble running the majority of homebrew software, you will not be able to run DSDoom. This is not the fault of the DSDoom developers.
In order to set up DSDoom simply copy the contents of the latest archive from the downloads page to your media device. Early versions needed these files on the root of the card but the latest builds been updated so that any device which supports the argv protocol should allow running from anywhere on the card. If your device does not yet support argv please complain to the manufacturer until it does. In the meantime you could use hbmenu.
With the latest hbmenu you can build command lines to pass to DS Doom which means you have access to all kinds of goodies like PWADS, DEHs and warping to specific maps. Simply create a file with a .argv extension in your DS Doom folder then edit it with a text editor. For instance an argv file containing
dsdoom.nds -iwad doom2.wad -file KDiP.wad -save KDiPwill start dsdoom with the doom2 wad, the Knee Deep in Phobos PWAD and place the save files in the KDiP directory.