The recoll program provides the user interface for searching. It is based on the QT library.
Start the recoll program.
Possibly choose a search mode: Any term or All terms or File name.
Enter search term(s) in the text field at the top of the window.
Click the Search button or hit the Enter key to start the search.
The initial default search mode is All terms. This will look for documents containing all of the search terms (the ones with more terms will get better scores). Any term will search for documents where at least one of the terms appear. File name will specifically look for file names.
The fourth entry (Query Language) is described in its own section.
All search modes allow wildcards inside terms (*, ?, []). You may want to have a look at the section about wildcards for more information about this.
You can search for exact phrases (adjacent words in a given order) by enclosing the input inside double quotes. Ex: "virtual reality".
Character case has no influence on search, except that you can disable stem expansion for any term by capitalizing it. Ie: a search for floor will also normally look for flooring, floored, etc., but a search for Floor will only look for floor, in any character case (stemming can also be disabled globally in the preferences).
Recoll remembers the last few searches that you performed. You can use the simple search text entry widget (a combobox) to recall them (click on the thing at the right of the text field). Please note, however, that only the search texts are remembered, not the mode (all/any/file name).
Typing Esc Space while entering a word in the simple search entry will open a window with possible completions for the word. The completions are extracted from the database.
Double-clicking on a word in the result list or a preview window will insert it into the simple search entry field.
Note that, apart from wildcard characters (single ? characters are ok), you can cut and paste any text into an All terms or Any term search field, punctuation, newlines and all. Recoll will process it and produce a meaningful search. This is what most differentiates this mode from the Query Language mode, where you have to care about the syntax.
You can use the Tools / Advanced search dialog for more complex searches.