Hi,
you can’t search for keywords as text because they are not text entries (unlike notes for example or clip names).
But you can search for certain keywords when you click on the magnifying glass on the upper right hand corner of your clip browser. Under the plus sign is a list of search criteria you can add and this search is of the boolean kind : is/is not, contains/does not contain etc, much the sae way as setting smart playlists in itunes. Very powerful.
You can then save that search in the form of a Smart collection.
If you recently transitioned from FCP7 I strongly suggest either a read of the manual or some video training such as Ripple’s or a course. It will save you lots of time in understanding these fundamental behaviours of FCPX.
Hope this helps.
Patrice Freymond
Editor  Certified Trainer FCP7/X
Post Consultant
Always learning…