HI there,
SO, the @toastee0 man , pointed you in the best direction and It’s FREE go join up and watch those 
WEBinars you’ll be glad you did. So to answer your question, the “dk” version is the Nordic Dev board of the MCU , they always end in “DK” i.e. Development kit. SO when you build samples or demos, do a two step. Build for the "DK " target to quickly get a sense of what is working and what might be missing.
Nordic actually TESTS there sample and Demo’s for accuracy and correctness with the documentation. They LEAD the industry in ALL of IT! (quiet peanut gallery 
)
With that method and some experience you’ll get up to speed fast.
You always have choices on the target just select the one without the DK in the name.
What dev environment are you using? I recommend the Nrf_SDK in Visual Basic studio. Easy to setup and get going, follows all the tutorials.
Open the terminal in the SDK and your all set to issue West build commands and it’s even easier. to rinse and repeat and really gain some traction.
I have some demo’s and examples of the setup and environment builds I use ,give them a look too.
there are others too. So be patient it’s a small learning curve, WE were all NOOBS at one time or another. that’s why WE are here… 
HTH
GL 
PJ 
build with the correct Targets, the first one is the Xiao, the second is the DK board.