The way numbers were talked about in Latin isn't much different from how they're used in related Indo-European languages--the most notable difference is the normal phrasing of numbers after X that end in -VIII and -IX.

For instance, instead of "Twenty-eight" and "twenty-nine" a Roman would say "Two-from-thirty" and "one-from-thirty." (Other Romance languages use subtraction with counting systems and/or telling time, so this is unique but not unusual).

Considering how complicated the rest of the language is Latin has a pretty standard and straightforward base-10 number-to-name setup. Here's a few numbers and how they're said in Latin:

VIII octō

XX vīgintī

XXVIII duodētrīgintā / vīgintī octō

XXXIII trīgintā trēs

Some numbers get different words if they're being used cardinally (one, two, three) or ordinally (first, second, third). The Romans described their dates ordinally but would use Roman numerals to write them.

Here are a few examples of how this worked grammatically in Latin, and what the equivalent numerical system produces in English:

I ūnus 'one' | prīmus 'first'

II duo 'two' | secundus 'second'

X decem 'ten' | decimus 'tenth'

XXI vīgintī (et) ūnus 'twenty-one' | vīcēsimus prīmus 'twenty-first'

The way the Roman numeral system is written is famously long-winded. It's easy to see why they weren't using it to dive into mathematics. But all that really mattered was that it made communicating, trading, etc. easier.

Only a handful of very commonly used numbers--1, 2, and 3; 200, 300, etc.--could change noun class (Latin has 3 noun classes, or "genders"--masc. fem. neut.) and/or grammatical case (subject of the sentence, possessor of something, etc.) Like cardinal vs ordinal usage, this difference would be reflected when the number was uttered aloud or fully spelled out, and it would be written with the same Roman numeral. The other numbers don't change noun class or case.

A brief note on Latin pronunciation in general: It's our best guess, based on prescriptive sources on Latin grammar, spelling changes over time, etc. "Rules" normally don't matter to linguists as much as how the language is actually observed to be used but in this case, the Romans' own documentation has been fairly helpful in letting us know what Latin sounded like.

Edit: Fixed formatting which was terrible on mobile!