Written accents (a less formal term than diacritics, which is a more technical term for the same thing) are marks made in writing or in printing to indicate how vowels should be pronounced, or similar functions. They are usually as fixed in a given language as the sounds of the letters. In English, there are normally no accents. When academics use words from foreign languages which DO have accents, they like to use the accents in the same way as in the original language. It is a kind of showing off how much the academic concerned knows. So you should try to use the foreign accents as well as you can. (For a list of those words covered in this guide, see Category:Foreign words.)
Examples of accents in European languages commonly known in English include the acute (´ as in á [Á] or é é [Ế]) and the grave (` as in à [À] or è [È]). (The word grave in this sense is pronounced in the French way: 'grahv', IPA: /grɑːv/.)
OED (1989) said s.v. accent, n 2.b.: "Marks used to distinguish the different qualities of sound indicated by a letter, called diacritical accents", and gives the following note: "The old ´ ` ˆ are mostly used, as French e é è ê in je, été, tiède, même, but a great variety of other signs have also been introduced. These diacritical accents sometimes distinguish meaning only, as French a à [a is the French for '[he] has'; à is the preposition 'to'. They are pronounced exactly the same], la là [in French, la is the feminine form of 'the'; là means 'there'; again, they are pronounced exactly the same]. These marks are not used in English orthography. But sometimes ` is used to show that -ed is to be pronounced as a distinct syllable, as learnèd, hallowèd, and some write é for a final e pronounced, as Hallé (properly German Halle)." (See also diacritics.)
If you need to use written accents, probably because you are quoting foreign words or learning a foreign language, it is easy to do so in Microsoft Word -- and all good word-processors: see typing accents.