In the Pattern box enter the known letters and dots for unknown letters and then hit return or the Lookup button.
For example: h.lp.r will return helper
Choose the Dictionary you want to use. The lower down dictionaries contain more words but some may not be proper words.
For more advanced word searching try Anagram Helper
Note that I have limited bandwidth so if this gets too popular it may go away without notice.
Contact me at craig@treefish.com