Continuing the discussion from Core v2.7.3d - More than 100 essential commands for your server!: I need help! I can’t find the area where I can edit all the custom join messages, afk timeout settings and more. Please if you know how to edit the configurable things in core reply with a solution. I am wondering if it is same as bukkit but can’t find the config.yml file anywhere
There’s no config.yml, this is not Bukkit 
Have a look at the /config/ folder, the plugin config should be in there.
Core has its own (very well written) wiki on github:
I looked inside the java file and i could only find .class files no config folder or config file. Do i have to run it on a server first to generate the file?
I believe yes. As already said: there should be a /config/ folder inside your servers directory. You don’t need to open the jar to edit the config Just put Core on your server, fire it up and have a look yourself.
EDIT:
Note that Core probably won’t run on SpongeForge BETA, as it hasn’t been updated in 2016 yet.