Another site that does Divi Tutorials; Divi4U has created a Child Theme Creator. Instructions are on the site but here they are for reference:
Divi Children gets installed just like any other plugin:
Download the plugin zipped file from the plugin page and save it anywhere in your computer.
From your WordPress Admin area go to Plugins > Add New.
Once on the Install Plugins page, upload the plugin file to install it.
Activate the plugin.
You then just fill in your little deets and its all ready to go.
The reason you want this is so you can add a ‘layer’ over your Divi theme where you put all your code tweaks and this keeps the original theme nice and safe from conflict :)
Now that that’s done, we can talk business…