There are many ways you can organize your research in Zotero.
In terms of research, think of libraries as your entire semester or your biggest research project; think of collections as individual courses in your semester or the various topics covered in your research project.
To create a new collection or library, select the New Collection or the New Library buttons in Zotero and create a name for your new folder.
To move resources to collections or libraries, drag and drop citations from the main list to the folder you want.
Using tags is another way to help organize and find your research. One left side of your Zotero window, near the bottom, there is a tags library. This tags library will reflect all of the tags assigned to the items that are currently displayed in the center. As you move throughout your library and display different collections and subcollections, the tags library will change.
Adding a tag to an item:
By default, Zotero will import tags with items that are added from databases. This means that your tags library will very quickly become unwieldy to manage because 5 - 30 tags will be added with every item from a database. Leaving the automatic tags setting on can be a challenge if you'd like to use the tags to add your own organization. To turn off the setting:
Another way to organize your research, is to create relationships between items. Zotero features a tool called Related Items. Related Items are created by beginning in an item and selecting another item that it is related to.