So do i, the only way to figure these things out is to get them wrong. Repeating the same lesson over and over is really demotivating... Sometimes i just leave it for the next day rather than continue.
At the very least give a description of new words/grammar being introduced. I thought there used to be grammar descriptions for some levels, not sure where they went though.
I've been struggling with this too, but I think what I've figured out is that the -o endings on these sorts of words (disso, nisso, naquilo, daquilo, aquilo) is used when the word is the sole object, rather than connected to another noun. For example, "I think about that" (w/undetermined meaning) = "Eu penso naquilo." "I think about that dog" = "Eu penso naquele cachorro." "I think about about that turtle" = "Eu penso naquela tartaruga." I'd appreciate it if a native speaker (or someone further along than me in Portuguese) could confirm/deny this theory.