The letters and sequence of the German alphabet are nearly identical to the English.  However, German has four letters that English-speakers may find unfamiliar.  Three of these are the umlauted vowels:

Ä / ä, Ö / ö, Ü / ü — Although the two dots above each vowel transform its sound into something wholly un-English, on keyboards not featuring umlauts these letters can be conveniently represented as ae, oe, and ue, respectively. Thus the word schön (meaning "pretty") can also be properly written as schoen, and thus avoid confusion with schon (meaning "already").

ß — While this might appear to be a misplaced Greek b (beta), it is actually an alternate form of ss (also sometimes written sz, and therefore called ess-tzet).  When encountered in a word such as muß or außer, the ß is pronounced as an unvoiced ss, as in massive.  Likewise, on keyboards without the ß character, it should be transliterated as ss.  It is a mistake to write a German word, such as groß (meaning "large" or "grand") as grob (meaning "coarse" or "rude;" it should be spelled gross.  That way we avoid such embarrassments as having our Großeltern / Grosseltern (grandparents) become Grobeltern (crude parents)!  The letter ß exists in the lower-case form only; when writing a word in all-capital letters, one should replace ß with SS.  Thus, Straße may (perhaps on a highway sign) become STRASSE (never STRAßE).

Another facet of written German that often strikes non-Germans as peculiar is capitalization.  All German nouns are capitalized, while modifiers typically are not.  Thus, "The American man rides in a German car" is properly written in German as "Der amerikanische Mann fährt in einem deutschen Auto."