A tag can be a single word or a phrase (which can include spaces). A phrase does not need to be surrounded by quotes: just type it as it is.
To search using more than one tag, each tag *must* be separated by a comma (we need the comma as spaces are allowed in tag phrases). For example:
To search for Hawkmoon OR Elric, type the following and then press "search"
To search for Hawkmoon AND Elric, type
To search for Hawkmoon NOT Elric, type
To search for Hawkmoon OR Elric but NOT Behold the Man, type
Hawkmoon, Elric, -Behold the Man
Note: if you type a + or - symbol before the first tag, it will be always be ignored