Hmm, how to explain that...
A direct object is an "external" object, so the thing/person directly affected/acted upon, as in e.g. Alcumenam adloquitur, "He addresses/talks to Alcumena", whereas an internal object is not something you act upon but something that is inherent in the action of the verb. It can be either what's called a cognate accusative — so a noun that is related to the verb as in, e.g. pugnam pugnare, "to fight a fight", or magnam insaniam insanire, "to be mad with a great madness" — or a neuter pronoun, as in si quicquam me amas, literally "if you love me anything", i.e. "if you love me at all", or Alcumenam multa adloquitur, more or less literally, "He addresses alcumena (with) many things/words". The same principle is at play in adverbs that are actually neuter accusatives like multum, satis, parum and such.