Login to the site where you want to use the Share Folder

Go to: Admin or Dashboard > Publishing > Folders
 
Click on Share Folder
 
Tick the box of the folder you would like to Share and click Save

Apply access to the folder for your Security Group

Select your Security Group

Go to Folders

Search for the Folder your have shared and apply your permission

ie.

• No Access
• Read Only
• Read/Write
• Full Access

Click Save