You can enter single or multiple terms in each search field. Use a space to separate multiple terms.
Search with all of the words If you enter multiple terms, separated by a space, the results must contain all terms.
Search with the exact phrase Only documents will be found containing the phrase in EXACTLY this order (maybe there are none or only very less hits as a result of this).
Search with at least one of the words If you enter multiple terms, separated by a space, in the field "with at least one of the words", the results must contain either one of the terms and may also contain several or even all of them.