I assume you’re writ­ing in Amer­i­can Eng­lish, but you might still encounter accented char­ac­ters in for­eign words. For­eign words arise in two sit­u­a­tions:

1. In proper names, like peo­ple and places (Albrecht Dürer, François Truf­faut, Plá­cido Domingo). In names, accented char­ac­ters must always appear accu­rately. Oth­er­wise, the name is mis­spelled.
2. In loan­words used in Amer­i­can Eng­lish. Some of these words have become nat­u­ral­ized cit­i­zens and should be spelled with­out accents (naive for naïve, melee for mêlée, coupe for coupé). Oth­ers have not and should not (cause célèbre, piña colada, Göt­ter­däm­merung). Check a dic­tio­nary or usage guide.

The inside back cover of the book has a table of the most com­mon accented char­ac­ters and how to type them. (But you are not hold­ing the book. Maybe you should order it.)