As described under "Organizing Your Library," tags can be added by hand or automatically imported with items.
When you click on any tag, the center column updates to display only the items with that tag. You can select multiple tags to further refine the results. To remove the filter, click on the tag again or choose "Deselect All" from the drop-down menu.
Use the search box in this pane to look for tags in the list.
Right click (Ctrl-click on Macs) on a tag to rename it across all the items or delete it from all the records it is attached to.
The tag selector pane defaults to only showing the tags of items selected in the Library. Choosing "Display All Tags in This Library" from the drop-down menu will make all the tags visible. You can then apply existing tags to items by selecting the items in the Library pane and dragging them onto a tag.
If you have not turned off the "Automatically tag items..." option under Preferences and you want to globally remove tags that have been imported with your items, choose the "Delete Automatic Tags in This Library..." option from the drop-down menu.
Sorting is a quick way to locate items in your library and collections. To sort, click on any of the information categories listed at the top of the center column. Change the categories displayed by clicking on the icon in the top right corner of the column.
The search box at the top of the Zotero application will look through all of your data for results, including tags, notes, and the full text of website snapshots.