Zotero allows you to organize your records into folders and sub-folders called collections and subcollections. You can create as many collections and subcollections as you want. By default, new records you import will be contained in whichever collection or subcollection you currently have open in Zotero.
To create a new collection, click the folder image with the green circle and white plus sign in the Zotero toolbar.
The new collection will show up under My Library.
Subcollections can be created by right clicking on a collection or subcollection and selecting “New Subcollection…”
Collections and subcollections may be organized by dragging them within the collection tree. If you want to make a subcollection into a collection, simply drag it to “My Library.”