Searching in the dictionary is rather simple. If you don't want to perform any special searching just type the word into the text field you are searching for, hit enter or click the 'Go' button and the searching process will be started. One more thing: While you are typing into the text filed, a panel will appear right below the text filed with some radio buttons on it. This is the expression chooser.
Please check whether the Wildcards button is selected. This is the default settings. That's all if you know how the word is spelled you are looking for, or if you don't want looking for a group of words, for example all words that end with apple (apple, grapple, pineapple, toffe-apple etc.) If you want to do things like this latter read on!
 
Note, the examples below were borrowed from the English-Hungarian plugin, so if you would like to try them out use that plugin.
Probably wildcards sound familiar for you. It was used in DOS (you know that crap stuff from Bill G.), but it is used in windows, too (another Bill G. classic). However, these wildcards are very useful, and very simple to use. The '?' character will substitute one character, and a '*' character will substitute one or more characters. With these two special characters you can do useful things:

Let's search for words which end with 'apple'! You just type this into the text field:
*apple
And the result will contain the apple, grapple, pineapple etc., and some terms with these words.

If you search the words which start with 'full':
full*
The result will be rather big, containing full, fullness, fully, full-blood etc. and a lot of expressions with these words. Quite big result, but you can use those output type chooser arrows below the result table to split the result into parts. For instance into expressions and words.

You can use more than one '*' characters in the text field. Try these:
*full*
j*ese

Let's play a bit with the '?' character. Remember it will substitute only one character. The next example will show the word that consists of 9 letters, but only four letters are known: the 1st letter is 'p', the 4th is 'f', the 5th is 'e' and the 7th is 't'. So type this into the text field:
p??fe?t??
The result will be the perfectly. Are you solving cross-word puzzles? :)

If you are looking for the Hungarian word 'fúrógép' but your keyboard doesn't contain those funny characters like 'ú', 'ó', 'é' etc. you just type this:
f?r?g?p
You can combine the * and the ? characters.
 
This is the third radio button on the expression chooser. When you select it, the so called combo box will be active and when you click on it, four chooses will appear:
Here you can set which part of the word you are looking for the text you typed into the input field. For example: if you type into the input field the word: apple and select from the combo box the 'The given word isn't complete (End)' then push the 'Go' button you will get all the words that end with apple. (And some expressions with these words.) If you had selected the wildcards method and typed into the input field: *apple you got just the same results.
 
This is the most complex method. Regexp (Regular Expression) is the standard UNIX pattern matching language. Regexp in this plugin allows you to construct a pattern for the words you are looking for. If you are not familiar with UNIX then it isn't worth getting involved in regexp. Probably wildcards will do its job very well. This function was designed for UNIX users, who know regexp.
For list of Regexp special characters click here.