Need help making a mod

Im bran new to making mods i watched youtube videos i tried to make one and i failed lmao

i used a mod call started bunndle. you start with a box you open it you start with basic things and its server side. i liked that idea to be able to reuse on a restart.

I tried to edit the mod didnt work so thats when i tried to look into making mods and tried to do it myself and failed and i cant figure it out lol

So when i edit the mod like just the name of one of the items it changes to were most the items dont spawn in

any pointers? or maybe anyone that would be able to make a mod? lol