Zotero allows you to easily create folders in order to organize your research citations.
Grouping items into folders
Click the "New Collection..." button on the upper left side of your Zotero pane to create a new folder.
Now you can drag and drop your resources into the appropriate folder. This is a great way to organize your research sources according to particular assignments/projects that you're working on.
In the "Info" pane on the right-hand side of your library, you'll see several tabs. The "Tags" tab allows you to add tags to individual items. This can be another helpful way to organize your material. (When you click on this tab, you may notice there are some tags already present. Zotero usually pulls these from any "keywords" associated with the item when the citation is extracted.)
You can use the tags however seems best to you. The best thing about tags is that they are searchable -- so you can easily find all the items marked with a particular tag, no matter which folder(s) they're in.
There are several ways to configure your Zotero desktop software preferences to customize your experience. To explore your preferences:
A pop-up window will appear with several types of settings to explore: