As archives contain primary sources, some which are not in written form, keyword searching can be difficult. You may find it easier to start by browsing a collection and focus your search as you get a feel for it.
If you want to do a keywords search be mindful that the more keywords you add the narrower your search will become. A useful technique can be to start with a basic keywords searching using either the subject, geographic location, format, creator or creation date. You can then choose to add more keywords to your to search to narrower it further.
Many archives have finding aids. These are guides, or keys, to help you navigate their collections.
Finding aids will help you learn more about the collection to determine if it is relevant. They typically include: background information on the creator or theme of the collection, a description of the collection's content and organisation, and a breakdown of the collection's contents.
Example of a Finding Aid is the Archival papers of Neville Hill. This link is from Victoria University's library catalogue record, which provides a brief record of the content in the archive boxes. More detailed information on the collection can be view in the link to the box list.
The National Archives of Australia has a range of finding aids (research guides) that you can explore here: Research guides
Not all archives have been able to digitise their content due to time, expense, copyright restrictions and privacy. You may have to visit certain archives in person or contact the archivist to discuss what you are looking for. They may be able to assist you with getting something digitised if you cannot physically come into the archive.
How do you locate archives that might have materials appropriate for your research? Here are some useful links: