AND: finds pages containing two or more words or phrases. Eg. folklore and celts finds pages containing both folklore and celts. You can use + instead of AND if you like.
NEAR: finds pages in which two or more words or phrases are close to each other. Eg. folklore near celts looks for folklore and celts on the same page. Results are ranked in order of greatest proximity.
AND NOT: Excludes results with certain keywords and/or phrases. Eg. To find all instances of fantasy but exclude results with film, use: fantasy AND NOT film. You can use - instead of AND NOT if you like.
OR: includes pages with alternate words or phrases, eg. Bull OR Shetterly locates any pages that mention either Bull or Shetterly or both.