Enter words separately, i.e. blue boat, and you will access images featuring both words.
If you enter two words with a space and a dash immediately in front of the second word, i.e. blue –boat or yellow –flower , etc you will access images with blue or yellow in them, but not a blue boat or a yellow flower, etc.
If you enter two words, you will access images with both words first, then images with either word.
Try changing the words by making them plural or by adding "ing" ("boat" or "boats” or "boating")
To refine your search, try using more words, such as: apartment buildings large city
If you know the image file number, you may enter it in the search field.