You need to be admin to work with this plugin. There are no permissions as all players can earn Kill Streaks. I find it easiest to just work with the KillStreaks.json in /oxide/config to set the basic options and then o.reload KillStreaks to pick up the changes. These parameters are detailed on the main page. This includes how to set up streaks.
At the bottom of the file: /oxide/data/killstreak_data.json are the streak settings. You can add them via the gui or manually set them there.
Please give the instructions on the main page a read, and if you have a specific questions please feel free to ask.
Please do not bother Wulf, this is not his plugin and he is a super busy gentleman.