Do I have to use iPhoto?

My iPhoto library is a total mess because I tried to alter it by grouping pix by subject, or place, splitting, merging etc. Now I can't find anything. I would prefer a system using tags where I could label each pic with person, place, date, etc. How could I do this on a mac?

Also, on one occasion I managed to import a design which I had copied (paste special as picture) to a Word doc into iPhoto. Now I cannot remember how I managed this.