Prerequisites - .net core sdk 2.0 - ffmpeg (and added to path) either download or install using your distro's package manager - git

Clone the repo
git clone -b 1.9
cd NadekoBot/src/NadekoBot
Edit credentials.json. Read the JSON Exaplanations guide on the left if you don't know how to set it up

run dotnet run -c Release

when you decide to update in the future (might not work if you've made custom edits to the source, make sure you know how git works)
git pull dotnet run -c Release