A wildcard is a symbol that tells the computer to accept any letter in that place. If you are not sure how to spell a term or there are alternate spellings, the wildcard will allow you to retrieve results. The most common symbol for this is a ?, but it can vary from database to database. You can check the help menu to see if wildcards work in any given platform.
gr?y retrieves gray or grey (alternate spellings)
wom?n retrieves woman or women (irregular plural)
Truncation literally means "cutting short." It allows you to put in part of a word and retrieve all the forms of the word that start with the characters you have entered. The most common symbol used for truncation is an *, but like the wildcard it may be different in different databases. Unlike the wildcard (which replaces a single letter and can be used in the middle or end of a word), Truncation can allow any number of letters and only works at the end of the word.
archit* retrieves architecture or architect
psycho* retireves psychosis, psychotic, etc.
Be careful not to over use truncation; many times if you cut a word too short you will get words that don't actually relate.
consum* retrieves consumer, consumes, consumerism
cons* retrieves all those words along with constipation, consult, constituent... etc.