Query language cheat-sheet. In doubt: click Show Query. You should really look at the manual (F1)

What | Examples
--- | ---
And | one two one AND two one && two
Or | one OR two one || two
Complex boolean. OR has priority, use parentheses where needed | (one AND two) OR three
Not | -term
Phrase | "pride and prejudice"
Ordered proximity (slack=1) | "pride prejudice"o1
Unordered proximity (slack=1) | "prejudice pride"po1
Unordered prox. (default slack=10) | "prejudice pride"p
No stem expansion: capitalize | Floor
Field-specific | author:austen title:prejudice
AND inside field (no order) | author:jane,austen
OR inside field | author:austen/bronte
Field names | title/subject/caption author/from recipient/to filename ext
Directory path filter | dir:/home/me dir:doc
MIME type filter | mime:text/plain mime:video/*
Date intervals | date:2018-01-01/2018-31-12 date:2018 date:2018-01-01/P12M
Size | size>100k size<1M