I understand that the keywords are important in search,my question is ,are they that important in content network too. thanks
The individual keywords - less so, because content uses the keywords together to establish the theme of your ad group. It will also only use 50 keywords per adgroup to ascertain this, whereas in a search campaign, however many keywords you have all get used to trigger ads separately. This is another reason why you should always have content and search as separate campaigns. You can, of course, decide to have placement targeting instead, where you decide to advertise on specified sites without being triggered by keyword matching, or a mix of the 2.