It is a very powerful method to expand the number of keywords, so use it carefully.
Add keywords you want to synomized
Paste the keywords you want find synonyms for in the left box (One keyword per line).
Choose the language from the drop down menu above the input box.
Choose the vocabulary data base from the drop-down menu to the right above the output box.
Click Start and wait until it finish. The process is finish when it you see: Input: Done
In the Advanced Setting you can choose your input and output keyword list from the drop-down menu. The keywords from the input keywords are taken from the Good keywords and the output is processed as unsorted keywords.
You find the output keywords as a task (promising/questionable) and in the output box.
Maximum words in keyword: Are a method for you to control the number of words you want to have combinations of keywords found for. If it is a long keyword it can be quit many combinations.