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, a wildcard will allow you to retrieve results. The most common symbol for this is a ?, but it can vary between databases. You can check the Help menu to see if wildcards work in any given platform.
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 asterisk (*), but it may be different across databases. Truncation can allow any number of letters, and it only works at the end of a word.
Be careful not to over use truncation. If you cut a word too short, you will get words that don't actually relate.