Before asking, read this.

-Do I need a new world?
If you want the ganja bushes to be spawned on worldgen, yes.

-Where I can find ganja bushes?
Ganja bushes spawn on forest biomes, crappy and dark ones more.

-How can I harvest ganja?
Use the shovel on bushes or use the razor when the bush is full of buds.

-How I got ganja seeds?
seeds drops from old stages of the plant when harvesting. Early stages wont drop.

-Where are the crafting recipes?
By default you can find on the mod tab.

-How do I dry the ganja?
Use the drying rack

-This mod will work with old saves?
Maybe, but they will not spawn ganja bushes on your world. You will need to use the console to spawn some seeds to start. c_give("ganja_seeds")

-All player need the mod to play on a server?
Yes.