Zotero can much more than just harvesting and inserting references, and if you are consistent about the use, it can serve as a 'digital study secretary' and be your one-stop-shop for working with literature, reading lists, notes and group work.
Zotero works with Google Docs - we recommend using it in Google Chrome. Also note, that it can take up some extra bandwidth, so avoid 'stressing' the system by inserting too many references too fast, and allow it to update in between working with your references.
By importing your PDF files into Zotero, you can read them straight from your reference (double click on the attached pdf), highlight text in different colors, and insert notes. Some PDF's will come on its own when you harvest the reference from a library or database source, others will have to be downloaded and drag-and-dropped from your device.
In the right hand panel, you will have tabs for writing notes to each reference, and you can 'tag' your references with keywords. Some keywords will be added from the publishers, but you can add your own as a tool for managing your references. The keywords or tags will be searchable from the top search bar. Also think of the pre-added keywords as inspiration for further searches in the same topic.
You may run into the risk of importing the same reference two or more times, and to avoid adding notes or tags to different versions, you can 'merge' the double entries by using the tool 'Duplicate Items' in your left side panel. Merging the files will avoid loosing content.
Creating folders and sub-folders can help you stay organized as you work in Zotero. The folder you are actively engaging in Zotero will be the one your are importing the references into from your browser, and doing so can help you group your references from the start. It will also allow you to clean out your Zotero library when you are done with an assingment or a course, and can help clear out storage space. Just remember to right click and chose 'Delete collection and item' to delete both the folder and all the references in it.