Enter word, and press Find :-)
Words you should use as search entries are case sensitive (usually lowercase, but proper nouns or German nouns are titlecase), and diacritic signs are important. If you do not have the ability to enter correct diacritics, you can select Input encoding Plain ASCII. Then the searching will disregard diacritics (and in some dictionaries will change to case insensitive). In Esperanto dictionary, it will expect words enterred using post-x method (sx cx gx jx hx ux), and in Russian-English dictionary it will expect words transliterated into ASCII.

Be sure to choose correct Input and Output encoding - utf-8 is ideal and supported by most modern browsers, but ASCII is a safe bet, if you have older browser or lack suitable fonts.

There are different searching strategies available:

exact
exact match
prefix
find words beginning with given string. For example, "wo" will find "word" "work" "working" ....
substring
find words containing given string anywhere in them. For example, "bst" will find "substring" "obstacle" "substance" ...
suffix
find words ending with given string. For example, "ing" will find "searching" "making" "sleeping" ....
fnmatch
find words using * and ? as wildcards. For example, "wor?" will find both "work" and "word", "f*er" will find "fellow worker" "fighter", as well as...
re
POSIX 1003.2 regular expression search. Modern regular expressions are the ones used by grep(1). Use * to match a sequence 0 or more matches of the previous atom; use + to match a sequence of 1 or more matches of the previous atom; uses ? to match a sequence of 0 or 1 matches of the prevous atom; used ^ to match the beginning of a word, uses $ to match the end of a word, and allows nested subexpression and alternation with () and |. For example, "(foo|bar)" matches all words that contain either "foo" or "bar".
soundex
The Soundex algorithm, a classic algorithm for finding words that sound similar to each other.
metaphone
Similar to Soundex, but using stricter similarity between words. Both soundex and metaphone are really good only for english words.
lev
The Левенштейн algorithm (string edit distance of one). This algorithm searches for all words which are within an edit distance of one from the target word. An 'edit' means an insertion, deletion, or transposition. So, e.g. words "work" "sword" have both edit distance one from word "word"