Truncation is just a library term that you use for simplifying a search.
How do you do it?
Normally when you type in a term in to google, say you type in child, it will bring back results with child or children.
Databases do not work that way. If you wanted to bring back the same results in a database you would have to put in the search box: child OR children.
That can be a lot of work, so library specialists have come up with a solution. Find the part of the word that is similar in both words, and that happens to be child, and put an asterisk * after the word, like this: child*. This will bring back all forms of this word now.
There are other rules that can also be used. If you are looking for the word anesthesia in a journal, you may pull all American Anesthesia articles, but you will not pull articles from countries that use the spelling Anaesthesia. So how do you get both spellings when you search for this word with having to spell out both? Use a question mark '?' as a place holder for the letter that may be there. For example: an?esthesia will bring back both variations in your search.