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> Most people are taught to study lists of words by themselves: apple, surrender, enormous. But when you learn words by themselves, a few things happen:  
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>  - You learn what the words mean, but you don't learn how they're used. You don't learn **what** other words they fit together with.  
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>  - The words get saved in your brain one by one. So when it's time to make a sentence, you have to pull them out again one by one. That makes it slow.  
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>  - You don't get a real connection to the words. They're just boring words in a list, so it's easy to forget them.
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I asked an English native speaker and he said that this phrase could be equally used both ways—with "what" or without it. Actually, without it, the sentence makes more grammatical sense to me. I have no problem reading it. But I can't quite understand it when there's "what". Could you please explain why it is there?