"Want" and "want" have what distinction, how to tell a student to listen to?

Before you begin, read these sentences:
I'd like to buy a pair of leather shoes.
I want to buy a pair of leather shoes.
I want to help you, but I can't. (X)
Teacher, I want to ask you a favor.
Xiao Lin, I have a favor to ask you.
We invited him several times, but he didn't come.
I didn't want to go, but they kept inviting me and I went.

在开始释疑前，请你先读读下面的句子：

（1）我想买双皮鞋。

（2）我要买双皮鞋。

（3）我想帮你，可是我也没有办法。（X要）

（4）老师，我想请你帮个忙。

（5）小林，我要请你帮个忙。

（6）我们几次邀请他来，可他就是不来。

（7）我本来不想去，可是他们一再邀请，我就去了。

[question]
What's the difference between "want" and "want"? When expressing a personal wish, can you say "no"?

【疑问】

“想”和“要”都可以表达个人愿望、打算，它们有什么不同？表达个人愿望时，可不可以说“不要”？

"Clear up a doubtful point"
"Want" and "want" are different in tone when they express a personal wish or intention.
"Think" has a slightly weaker tone, it just means that the person has this idea, has this intention, but does not go to do it is not certain.
"Want" is very strong, when "want", the speaker's tone is very determined, often express a very strong desire, or a decision, determination, the speaker will generally do the same.
I want to buy it. I want to buy it. I want to buy it. I decided to buy it and I will buy it. I have the idea of helping you, but I can't. You can't use "want" here, because if you use "want", it means "I" decided to "help you", instead of "can't help".
Because the tone of "want" is weak, so when we make a request to others, use "want", it is polite, polite; If you use "want", you sound casual. You should be polite to your teacher. You can make yourself at home with your friends.
It's important to note that when we say we don't have an idea or intention, we usually say "no" and "don't want" instead of "no." "Don't" is used to discourage or discourage others from doing something. Like "want" and "want", "no" and "don't" have different tones. No, no, no, no, no, no, no, no, no, no "Don't want to" is a weaker word, just saying a thought, for example (7).
Because "think" and "don't" are both weak, they can be preceded by "very", "compare", "a little", etc. "Must", "must" and "never" can be used to express a more assertive tone.

【析疑】

“想”和“要”在表示个人愿望、打算时，它们的语气不同。

“想”的语气稍微弱一些，它只是表示这个人有这种想法，有这种打算，可是去不去做还不一定。

“要”的语气很强，用“要”时，说话人的语气很坚决，常常表示一种很强烈的愿望，或者一个决定、决心，说话人也一般会这样去做。

如例（1），用“想”时，表示有这个想法，可是最后去不去买，还不一定。例（2）用“要”时，表示“我”决定去买，也就会去买。例（3）包含我有“帮你”这个想法，可是做不到。这里不能用“要”，因为如果用“要”，那就表示“我”决定“帮你”，就不会说“没办法”了。

因为“想”的语气比较弱，所以当我们向别人提出请求时，多用“想”，这样显得客气、礼貌；如果用“要”，口气就很随便。如例（4）对老师应该客气一些，所以用“想”。例（5）对朋友可以随便一点，可以用（要）。

需要注意的是，当我们表示没有某种想法或打算时，我们通常说“不”“不想”，而不说“不要”。“不要”一般用来禁止或劝阻别人做某事，相当于“别”。和“要”与“想”一样，“不”和“不想”也有语气的不同。用“不”显得很坚决，表示一种决心、决定，如例（6）；“不想”的语气弱一些，只是在说一种想法，如例（7）。

因为“想”和“不想”的语气都比较弱，他们前面都可以用“很”“比较”“有点儿”等表示它们的程度。而“要”和“不”的语气强，可以用“一定要”“非要”“决不”来表达更坚决的语气。