Olá, Riverc!
The (3rd person) object pronouns are o(s)/a(s).
When they are attached (w/a hyphen) to a verb form ending in -r, -s, or -z, then that final consonant converts into an -l...and forms the variant pronouns -lo(s)/-la(s).
Não o consigo ver.
Não consigo fazê-lo.
Já estudaste as matérias?--Não, ainda tenho de estudá-las.
Queres servir o vinho?--Sim, quero servi-lo.
Onde é que vocês encontraram os corpos?--Encontrámo-los na rua.
Como queres que o diga?--Di-lo com franqueza.
By the same token you have:
Fizeram-nas em enorme quantidade. (as bolachas)
Põe-nas na mala. (as coisas)
If you need more help, just click on my icon.
(Btw, what I've written holds true for both Brazilian and European Portuguese. The business which another posted referred to--of using subject pronouns instead of object pronouns--although common, is only true of uneducated, "popular" Brazilian Portuguese speech. It is not accepted at all levels of BP and certainly not in writing. And it is *never* accepted in EP, where it is considered a gross error.)