You can export an item from your library in order to use it in another software. Right click while one or several items in your library are marked to see the alternatives for exporting. For instance, if you want another user to be able to import the item to Zotero, you can export an item as RDF. If you want to use the item in a different citation management software, you can use RIS, which is supported by several programs.
You can import items that you have available, for instance, as RDF files on your computer. Choose File > Import (short command Ctrl + Shift + I).
Formats that are currently supported for import to Zotero can be found here (i.a., Zotero RDF, CSL JSON, BibTeX, and RIS).
Exporting your library
It is not recommended that you export your entire library using the export/import function, even if it is possible to do so (File > Export library and Import). The reason is that information may be lost in the imported library. Furthermore, the links to items added to documents created earlier will be broken. Instead, choose to synchronise your library or to copy the entire Zotero folder in the same way as when backing up your library.
Exporting to word processors and text editors
You can create a reference list without using plugins for different word processors, for instance if you want to quickly insert literature on a webpage or in a document.
As a suggestion, you can put the items that you want to use in the reference list in a separate folder in Zotero.
Exporting to Excel
In order to export items to Excel, you first mark the items that you wish to use in Zotero, right click to see the options for exporting, and choose the format CSV.