Sentence Structure Help!

私は昨日の晩にラジオで音楽を聞きました。

私たちは午後三時に学校を出ました。

あのその歌はよかったです、でも歌の名前はを忘れました。　It sounds more natural in this way. It is more common to use "それ" than "あれ" to refer to something that you mentioned in the previous sentence. Also, it's better to avoid using the same word twice in the same sentece. Sometimes, there's no other choice though. The change from "を" to "は" looks like a very simple correction but actually it is the toughest one and maybe it was unnecessary. But I'm sure most Japanese people would say "でも名前は忘れました" because you remember how the song goes or at least that it was a good song. In this case we usually speak about something we don't remember by contrast with what we do remember. Therefore, "は" sounds more natural.

私は「Lang8.com」で日本語の新しい（単語 or 表現 or 単語や表現）言葉を学んでいます。　Your original sentence was fine. However, it sounds a bit unnatural to me becuase Japanese itself is 言葉.

私は昨晩ラジオで音楽を聞きました。

あの歌はよかったです。でも歌の名前を忘れました。

私は「Lang8.com」で日本語の新しい言葉を学んでいます。

ありがとうございました。