Being nervous can sometimes make you rush because of adrenaline. 'That' refers to the fact I just mentioned. If you are aware that nerves can make us rush, it will be easier to slow down and give well thought out answers.

In this case, it helps to break what is being said down into pieces, because it's not being conveyed clearly. "The nerves can make you give a speedy, a speedy response, and what you want to do is be aware of that and just slow your answer down." Looking at the context, we can omit the second "a speedy", because it isn't being used for emphasis or in any meaningful way; it's more of a stutter. This is actually a complete thought on its own. "The nerves can make you give a speedy response." In other words, if you're nervous, you might answer too quickly, without thinking your response through. "What you want to do is be aware of that and just slow your answer down." This is what we have left. "That" refers to what was previously said, which is, "The nerves can make you give a speedy response." This part of the statement is not worded very well. "What you want to do is be" sounds very awkward. "What you want to do is" is a conversational way of saying that you should do something. It sounds less like an order, and more like a friendly suggestion. If we take away the conversational part, we're left with, "be aware of that and just slow your answer down." The more concise statement is as follows. "The nerves can make you give a speedy response. Be aware of that, and slow your answer down." Remember that being nervous can make you give an answer too quickly. Keep this fact in mind, and take your time to answer more carefully. In conversations and lectures, you have to use context to try to work around messy dialogue that doesn't really matter. You can focus on the key points, and as long as you are able to understand those, you can take away the most important information. :)

The subject (noun phrase) is "what you want to do". The main (finite) verb is "is". The predicate (the complement of a subject in a sentence with "to be") is "be aware of..." Here is another example: "What I would really like to do today is watch a film in the cinema."

ok.Thank you for your advice.

Did you mean "Why does 'is' appear?" The 'is' is _the_ verb. 'What you want is a slap' = 'The thing you want is a slap'. I think it's a form of passive voice. So, 'What you want to do is leave'. Also - please be careful with your punctuation: "sentence. And",