I have never added 'key words' before.
On the contact sheet I pressed the I button (bottom left) of the image
I then inputed my key words to the key words box.
And then pressed the 'save&' button to take me to the next image and repeated.
Is that it? Are the key words embedded?
Will my client be able to search using the key words they asked me to apply?
It depends on the kind of images you're keywording, and what software your client will be using to perform the search.
If they're JPEGs, TIFFs, PSDs, DNGs, or PNGs, then the metadata will definitely be embedded into the photos. If they're RAW files, then the metadata will either be embedded into the RAW files, or placed into an XMP sidecar file (a file with the same base name as the RAW file, but whose file name extension is .XMP).
Perhaps you could tell me more about your situation and what software your client will be using to search for keywords.
-Kirk