A key element of designing for usability is to assume that the user will be coming into the application with no previous knowledge of how it works. Most users don't read manuals or documentation, and the end users won't have you there to provide instructions or an overview. For testing, I agree that you should start the user "blind". However, you should also make sure that the system provides ample feedback to the user - if keywords are required, for example, make sure the program tells the user this and if possible also tells the user how to add the keyword (or make it possible to add the keyword from the same area of the interface, or as part of the same process).

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