How is the "b" in "lubi" pronounced? It's hard to hear it. Loobee, loopee, lookee, loong-ee?
the audio is strange, should be normal "b" ( like in "to be" )
I guess you should report wrong audio if you get this sentence again.
So you can never truly specify in Polish and just have to take it from context?
Yes. Sometimes "the girl" does mean more of "this girl" and therefore will be translated as "ta dziewczynka". But a/the distinction is not a point of interest for Polish.
What is the difference between cłopec and cłopcem? Yes i know it is wrong but please help me
"chłopiec" is the basic, Nominative form. It mostly serves as the subject of the sentence, like here.
"chłopcem" is Instrumental. For now it's enough that you know that it is used in sentences like "He is a boy" = "On jest chłopcem".