por the time of the Late Roman Republic the Latin alphabet consisted of 23 letters. All of them were capital letters:
A B C D E F G H I K l M N O P Q R S T V X Y Z

The pronunciation slightly differs between Classical Latin and Ecclesiastical Latin.

Classical Latin pronunciation
Vowels:
a – [a] - like in ‘cup’
ā – [a:] - long, like in ‘father’
e – [E] - like in ‘pet’
ē – [E:] - long, like in ‘pay’
i – [i,j] - like in ‘lip’
ī – [i:] - long, like in ‘leap’
o – [o] - like in ‘not’
ō – [o:] - long, like in ‘for’
y – [y] - like in French ‘tu’
ȳ – [y:] - long, like in French ‘sur’

Diphthongs:
ae – [ai] - like in ‘eye’
oe – [oi] - like in ‘oil’
ei – [ei] - like in ‘reign’

Consonants:
b - [ b]
c - [k] like in ‘cat’
ch - [x] like in ‘ham’
d - [d]
f - [f]
g -[g] like in ‘gag’
h - [h]
j - [j] as in‘yes’
k - [k]
l - [l]
m - [m]
n - [n]
p - [p]
ph - [p] like in ‘peasant’
qu - [kw] like in ‘quack’
r - [r] Scottish ‘r’
s - [s] like in ‘hiss’
t - [t]
th - [t] with sharper expulsion of breath
v - [w] like in ‘way’
x - [ks, gz] like in ‘wax’
z - [dz, z]

Ecclesiastical Latin
Differences:

Vowels:
u – [ u] - like in ‘pull’
ū – [u:] - long, like in ‘pool’
y – [ i] - like in ‘feet’

Diphthongs:
ae – [e] - like in ‘red’
oe – [e] - like in ‘red’
au – [au] - like in ‘house’
eu – [Eu] - like in ‘meoos’
ui – [wi] - like in ‘quid’

Consonants:
c - [k] like in ‘cat’
c - [ch] like in ‘church’
sc - [sh] like in ‘shed’
ch - [k] like in ‘ham’
h - is mute
ph - [f] like in ‘phone’
ti - [ts]
v - [v] like in ‘virgo’
z - [dz]

Not mentioned are read the same as in classical Latin.