I am not sure what you are heading for.
If you want to know how DS cheats are encoded (cheats tend to have a type*, an address they work on and what to write once you get there) then enhacklopedia
https://doc.kodewerx.org/hacking_nds.html
or indeed
http://problemkaputt.de/gbatek.htm#dscartcheatactionreplayds for a more succinct approach.
*newer devices tend to have more and more options. Most old cheats of the memory variety (basically everything like action replay, gameshark, pelican, codebreaker, goldfinger... except game genie which altered the ROM instead, hence comparatively fewer codes but more far reaching ones for that. Some did branch out into save dumping/editing in later systems still and technically the DS binary is in memory so you can do some quite radical what would traditionally be ROM altering cheats with memory cheats) would only do simple constant writes (maybe differing only in whether it is 8 bit or 16 bits that are written), later stuff allows you to do ranges, check if something happened and then act accordingly and all manner of other fun things like that.
If you want to know how to make cheats then it works much the same on all devices, though newer ones might change up the memory locations between runs (has been seen on the DS a fair bit as well, see pointer codes).
https://web.archive.org/web/20080309104350/http://etk.scener.org/?op=tutorial being my usual guide to it all for now.
It gets a bit more interesting when you go further into cheats. I mentioned in the passing the DS binary in RAM thing but before that there is moon jump (usually done by finding the "has jumped" for any double jump flag in the game and setting that to not done and thus jump to the sky becomes a possibility), character selection things (find what character values are, set to other things and this is how you get play as boss/hidden characters type cheats) and time saving approaches for inventory cheats (don't find the end game sword, find the basic starter town dagger and buy many as you should have infinite money, most games will either be a value indicating what it is and how many you have, or will be a location nearby as the game uses basically a giant grid and location on the grid determines what it is. Same idea for stats that might be hard to change normally like luck as they will probably be with that character's other stats or with all the other luck values for the party which will probably be soon after the last other stat).
If you want to know how to hardpatch the cheats into a ROM so they always are on (don't think that is what you are going for it but it is the other usual question) then
https://gbatemp.net/threads/ds-auto-trainer-maker-dsatm.80540/ does it for you.
https://gbatemp.net/threads/crackers-ds-trainer-maker-tutorial.44410/ covers a lot of it if you wanted to go manual. I do also have a worked example (albeit for the GBA, though the DS uses much the same CPU and approach) in
https://gbatemp.net/threads/gbatemp-rom-hacking-documentation-project-new-2016-edition-out.73394/
