It is not generally possible to reproduce such markings using a keyboard, but such symbols exist in most fonts nowadays. It is quite possible to insert them into e-mails or whatever else you may wish by copying and pasting them out of a word document. Simply insert the desired character into a word processing document and insert it where needed.
I often use this to insert accented characters or IPA symbols into postings, comments, and e-mails.
Here is a sample:
Voilà, j'ai une étoile dans ma poche! Il y a une château dans le forêt. Tu
es une amie chère. L'île est très belle. Aïe!
These symbols are the grave (à), acute (é), and circumflex (î) accents and the diaeresis (ï). In French orthography, they serve varying functions.
The grave is mainly used to distinguish homographs, which are usually also homophones, but it also changes the pronuncation of the letter "e" from [ø] to [ɛ].
The acute is used only on the letter "e" to effect the pronunciation as [e].
The circumflex is used to denote that a silent letter, usually an "s", has been omitted from writing, sometimes changing the sound of "a" to [ɑ:], "e" to [ɛ:], or "o" to [o:], or lengthening the sounds of "i" and "u".
Lastly, a diaeresis is employed to indicate that a vowel (in French, usually an "i") is sounded separately rather than part of a vowel digraph, as in the interjections "aïe" and "aïlle", pronounced [ɑ:i] and [ɑ:ij], respectively. Both mean "ouch".
I hope that this has been helpful to you.
One final note, the acute is used to mark stress in Spanish when it does not fall upon the penult or to distinguish homographs, usually in monosyllables.
A Spanish diaeresis is only used upon the letter "u" to indicate that it is sounded prior to "e" or "i" following a written "g".