From my view this are 2 two ways to activate an end device (node) [ In my case the gecko-board]
OTAA means Over-The-Air-Activation and ABP means Activation-By-Personalisation
This is given by the LoRa Alliance for security reasons. (1.0.2
Maybe this video will help you to answer your questions similar to the ones I have.
needs the DevEUI,AppEUI and AppKey for the device. The Server needs the AppKey
EUI stands for Extended Unique Identifier which is 64-bits long.
is similar to MAC address known in the network world like a unique name like “Tjark Ziehm”
is similar to an port number of a server… that your devices know where to go in your TTN instance.
The AppKey is an AES ( Advanced Encryption Standard) on 128 bit symetric to make sure that your messages from the node are secure.
If you are new to LoRaWan i recommend the videos
Thanks a lot to Mobilefish.com
I hope that I was able to help you, pls feel free to add more information