Sounds like you already figured it out, but for other people reading this:
The -aĵo suffix means "something made from or possessing the quality of"
porko (pig) ⇒ porkaĵo (something made out of pig = pork)
nova (new) ⇒ novaĵoj (things that are new = the news)
vesti (to clothe) ⇒ vestaĵo (something with which one clothes = a piece of clothing)
CloudeAytr made great a more in depth post about it here: https://www.duolingo.com/comment/8849511
I'm not entirely sure, but here's a link that explains -ajx.
It's modeled on how the Romance languages work. I see you're also learning Italian. It's the same rule. All adjectives must agree with the noun they modify, and this includes possessives. The only difference is that Esperanto only has one form of "the" and no gender.
la mia scarpa è piccola = my shoe is small
le mie scarpe sono piccole = my shoes are small
il mio gatto è piccolo = my cat is small
i miei gatti sono piccoli = my cats are small
mia ŝuo estas malgranda = my shoe is small
miaj ŝuoj estas malgrandaj = my shoes are small
mia kato estas malgranda = my cat is small
miaj katoj estas malgrandaj = my cats are small
As I said, possessives are a type of adjective, and all adjectives must agree with the noun it modifies. The first part of the word,
mi, says that "I" am the owner. The last part of the word says whether my thing is singular or plural (and in Italian, whether the thing owned is masculine or feminine).
His articles of clothing are black.. Weird way of phrasing it. I guess it's normal in Esperanto
No. Esperanto writing is one-to-one with pronunciation.