I live in Orange County California. I have four live Oak trees and all of them have a small green gourds growing. These are not acorns
These are called "galls," and are relatively harmless. Here's an article that
explains the condition:
https://www.gardeningknowhow.com/ornamental/trees/oak/oak-apple-gall-info.htm
while your site says it's easy it maddeningly doesn't say how. it just assume you have a tree and want to plant it. but how do you get a sapling?? is there a seed or can you cut a branch and will it root? thanks for any help!
These articles should help:
https://gardeningsolutions.ifas.ufl.edu/mastergardener/outreach/plant_id/ornamentals/live_oak.shtml
https://aggie-horticulture.tamu.edu/newsletters/hortupdate/2010/nov_dec/acorns.html
http://extension.msstate.edu/publications/growing-your-own-oak-seedlings
https://www.gardeningknowhow.com/ornamental/trees/tgen/planting-trees-from-twigs.htm