3. Those foreign diacritical marks ("accents")
Be aware that some words and names from most modern languages
(French, German, Spanish, Italian, Portuguese, Polish, Czech,
Swedish, etc.) require diacritical marks ("accents").
Your English-language spell-check will not check correct use of
these marks. However, your word-processor WILL allow you to make
them -- and you should do so. Diacritical marks are used infrequently
in English, mainly where a word from some other modern language
(that requires them) has been adopted into English.
Example 1: Johann Gottfried Huebner was
an 18th century German insect taxonomist. His family-name ("last
name") can be spelled Hübner, because "ü",
which is the letter "u" with a diacritical mark called
Umlaut* in German and diaeresis in English, is equivalent to the
letters "ue". Too many North American writers omit the
Umlaut, because it is strange to them, and spell the name "Hubner",
which has to be pronounced differently (compare the English words
hub and hue), and is wrong. This name can be spelled Huebner or
Hübner, but not Hubner.
Example 2: August Sallé was a 19th century
French taxonomist. His family-name is pronounced "SALL-AY"
and, to do this, requires an "acute" accent over the
letter e ("é"). Without the acute accent, it
would be pronounced "SALL" and would be incorrect for
his name (although some French people have the the family-name
Salle, which is pronounced SALL).
Example 3: the
letter "c" has two pronunciations in English: hard as
in "cat" and soft as in "cent." The "soft
c" is distinguished in French and Portuguese (before vowels
a, o, and u) by writing it with a cedilla "ç".
Omission of this "cedilla accent" makes the "c"
hard -- this diacritical mark must be used where it occurs in
Portuguese and French.
Example 4: the Spanish word "agrícola"
(= agricultural) is written with a diacritical mark ("acute
accent") on the letter "i" - otherwise the letter
"o" would be stressed (the penultimate syllable). It
is incorrect to write this Spanish word without the diacritical
mark.
Example 5: the Italian word "università"
(= university) is written with a diacritical mark ("grave
accent") on the letter "a" - otherwise the second
letter "i" would be stressed (the penultimate syllable).
It is incorrect to write this Italian word without the diacritical
mark.
Example 6: Brazil's largest city (in a state of
the same name) is spelled São Paulo. The name is Portuguese,
with English equivalent Saint Paul and Spanish equivalent San
Pablo. English-speaking people typically omit the diacritical
mark ("tilde accent") over the letter "a"
in São, and mispronounce the name as "SAY-OH PAW-LOH"
although in Portuguese it is pronounced "SAH-ONGH POW-LOH".
The diacritical mark is critical to the pronunciation of the first
word which therefore sounds much like the Spanish word "San"
and nothing at all like the English mispronunciation "SAY-OH."
Example 7: Adam Bøving was a Danish entomologist
who worked in the USA. His last name is pronounced BUH-VING. Without
the diacritical mark (slash or "stod" through the letter
"o") his name would be pronounced BOH-VING. Not all
U.S. typesetters who published his works had "ø"
in their character set, and so sometimes used the German "ö",
which has much the same "uh" sound.
Example 8: The family-name of Czech entomologist
Z. Boucek (for proper accent refer to figure below) is pronounced
BOO-CHECK because the diacritical mark over the letter "c"
makes this sound like English CH. 
Example 9: The English word canyon is derived from
the Spanish word cañon and has identical pronunciation.
In Spanish, ñ is considered a separate letter of the alphabet
(not a letter with a diacritical mark). The sound of Spanish ñ
is "NY" in English.
Diacritical marks ("accents") are important to
pronunciation. Use them where they are required. You CAN make
them on your word-processor.
*all German nouns are capitalized.