Esperanto has a twenty-eight letter alphabet, including six letters with diacritical marks. The letters with diacritical marks are ĉ, ĝ, ĥ, ĵ, ŝ and ŭ. The alphabet consists of these letters: a b c ĉ d e f g ĝ h ĥ i j ĵ k l m n o p r s ŝ t u ŭ v z. The alphabet does not use q, w, x, or y unless they are in untranslated foreign names. A number of commonly available fonts support the Esperanto diacritical characters. Among these are: Ariel, Calibri, Constantia, Courier New, Lucida Sans Unicode, Tahoma, Times New Roman, and Verdana.
Download the Esperanto diacritical characters in those fonts to cut and paste the correct characters when you type in Esperanto. Information in the description of the download contains suggestions for incorporating the characters into your spell checker dictionary.
If you are interesting using alt codes on your Windows PC to type the characters, information is available in this Esperanto Diacritical marks blog post.
Zamenhof also proposed a convention to allow the language to be used in printing (and now in computing). He suggested that the letters with diacritical marks have the symbols replaced with the use of ch, gh, hh, jh, sh, and u. Another more recent convention represents the characters with diacritical marks with the use of x, giving cx, gx, hx, jx, sx, and ux. This also allows for correct sorting of words beginning with those characters, as they will turn up alphabetically immediately after the words starting with the characters without diacritical marks, and also allows easy translation back to letters using the diacritical symbols.