Asalamo Alaikum. 
So, as the title suggests, I have questions about beards!
Is it Sunnah or Fard for guys to grow a beard?
What are the rules, if any, for growing a beard?
(regarding shape, size, etc)…
I have seen many people with a beard and a mustache, and some with only a beard and shaved mustache. Why the difference?
Re: Beards
The Muslim beard is to grow the facial hair, except moustache which is to be kept short ... Some people interpret this to mean that that beard must be at least visible on the face and moustache should be less than that ... Shaving moustache completely is allowed and leaving it with a bit of stubble is allowed ... So long as the hair strands do not over grow the lip line and end up in food and drink ... Some assert the proper beard as per Sunnah is to have it long enough to grasp with one hand and not longer than two fists and one extended handspan.
Basically the differences are down to interpretation.
Most interpretations are that the beard must be trimmed or levelled and tidied up ... But some people do not follow that view.
and Wassalam (thanks for reminder LLK)
Re: Beards
& Peace MM,
Clipping the moustache is also an act of fitra too. It is ‘Sunnah’ as well as an order ordered by the Prophet Muhammad 
Book ‘The Book of Purification (Kitab Al-Taharah)’ of Sahih Muslim. Hadith Nos. 0498, 0499, 0500, & 0501.
**Ibn Umar said: The Apostle of Allah (may peace be upon him) said: Trim closely the moustache, and let the beard grow.**
**Ibn Umar said: The Apostle of Allah (may peace be upon him) ordered us to trim the moustache closely and spare the beard.**
**Ibn Umar said: The Messenger of Allah (may peace be upon him) said: Act against the polytheists, trim closely the moustache and grow beard.**
Abu Huraira reported: The Messenger of Allah (may peace be upon him) said: Trim closely the moustache, and grow beard, and thus act against the fire-worshippers.