"He sees them."
Translation:Lui li vede.
Well, "them" in English is used for both the direct object and the indirect object. So use the definition which fits the sentence. "li" is only for direct object and "gli" is only for indirect object. "them" does not differentiate and does mean both, so the context matters. If you cannot put "to them", then don't use "gli" For example "I give them the dog." can be worded as "I give the dog to them." that would use "gli".
Vede is the conjugation of the verb vedere for 'he/she sees'. So the endings tell you who is seeing (in this instance, but the same with all verbs). There are quite a few patterns to get to know the endings, for example -iamo is always 'we', so you can automatically know that 'we see' is vediamo. Quite often you can just learn what each ending means and apply it to each verb.
However, you do have to be careful as there are some differences when the infinitive ends in -are and -ere, such as vedere and cantare, as they can have a different pattern when conjugated. For example they see is vedono, whereas they sing is cantano (different ending). Just a case of getting to know each verb and the patterns.
No, the word by itself "them" could be used as a direct object "li" or as an indirect object "gli". Every hint is not good for every sentence. Pick the one that fits the sentence best. If you had the sentence, "I give them a gift." then "them" in that context would be "gli" as you can also word the sentence as "I give a gift to them.".
This verb requires a direct object and not an indirect object. "a loro" is the emphatic form for indirect object. "loro" can be the emphatic direct object form. This would mean "THEM" as opposed to some other people. http://esl.about.com/od/grammarstructures/a/Indirect-Objects.htm http://italian.about.com/library/fare/blfare166a.htm http://italian.about.com/od/grammar/a/using-personal-pronouns-italian.htm
"Lui li vede." would be a common way to say "He sees them.", but it is not the only way. The tonic or disjunctive form "loro" can also be used for emphasis, but it would come after the verb. An example would be if you wanted to stress "THEM" rather than "you" or "us". "Lui le vede." would also be correct for "them" if they were all female. A mixed group of female with at least one male would also use "li" if you are not emphasizing. Scroll down here for the Tips and notes: https://www.duolingo.com/skill/it/Clitic-Pronouns-1
anch'io ho risposto: "lui li vede", poi quando ho visto che davano per giusto "Lui gli vede", ho avuto compassione per quella traduzione: io sto imparando, mentre qualcuno continua a sbagliare. Sono contento così. Mi servirà a non commettere gli stessi errori che già oggi ritengo errati.