on't worry, questions are always welcome!
It is within our nature to grow both beards and moustaches (if you are male that is!), the moustache is left because there is a difference between our nature and our natural disposition [fitrah]:
Narrated Abu Huraira: I heard the Prophet saying "Five practices are characteristics of the Fitra: circumcision, shaving the pubic hair, cutting the moustaches short, clipping the nails, and depilating the hair of the armpits." [72:779 Bukhari]
The beard is sometimes trimmed, the method is the grab your beard with your hand and anything that is longer is cut (although there is some dispute), to avoid looking messy. It is important in Islam to see the beauty in all things and to present oneself well. The importance of cleanliness can also not be stressed enough:
‘Abd-Allaah ibn Mas’ood, who narrated that the Prophet (peace and blessings of Allaah be upon him) said: “No one will enter Paradise who has an atom’s-weight of pride in his heart.” A man said, “What if a man likes his clothes to look good and his shoes to look good?” He said, “Allaah is beautiful and loves beauty. Pride means denying the truth and looking down on people.” [131 Muslim]
And as mentioned before, it is important to differentiate between Muslims and others:
"The ruler of Yemen, appointed by the Persian emperor Kisraa, sent two envoys to the Messenger (S) to summon him. When they came into his presence, he noticed that they had shaved their beards and grew their moustaches. He hated to look at them (because of their odd appearance) and he said: Woe be to you, who told you to do so? They replied: "Our lord! (referring to Kisraa.)" The Messenger (S) then said:
But my Lord, may He be exalted and glorified, has commanded me to leave alone my beard and to trim my moustache."