1. The letter u ultimately comes from the Phoenician letter
Waw by way of the letter
y.
2. U is also the source of the mathematical symbol ∪, representing a
union. It is used mainly for
Venn diagrams and
geometry.
3. It is used as for
micro- in metric measurements as a replacement for the Greek letter
μ (mu), of which it is a graphic approximation, when that Greek letter is not available, as in "um" for
μm (micrometer).
4. In
English, the letter ⟨u⟩ has four main pronunciations. There are "long" and "short" pronunciations. Short ⟨u⟩, found originally in closed syllables, most commonly represents
/ʌ/ (as in 'duck'), though it retains its old pronunciation
/ʊ/after
labial consonants in some words (as in 'put') and occasionally elsewhere (as in 'sugar'). Long ⟨u⟩, found originally in words of French origin (the descendent of Old English long u was respelled as ⟨
ou⟩), most commonly represents
/juː/ (as in 'mule'), reducing to
/uː/ after ⟨r⟩ (as in 'rule') and sometimes (or optionally) after ⟨l⟩ (as in 'lute'), and after additional consonants in American English (see
do–dew merger). (After ⟨s⟩, /sjuː, zjuː/ have assimilated to /ʃuː, ʒuː/.) In a few words, short ⟨u⟩ represents other sounds, such as
/ɪ/ in 'business' and
/ɛ/ in 'bury'.
5. You read none of that.