Sentence:  He also bought a huge square of pegboard for hanging up his tools , and lumber for his workbench , sandpaper and glue and assorted nails , levels and T squares and plumb lines and several gadgets that he had no <WSD>idea</WSD> how to use or what they were for . 
Meaning of the word marked with <WSD> tags:  the content of cognition; the main thing you are thinking about