Expressing want with 想 (xiǎng) and 要 (yào)
Generally, 想 (xiǎng) and 要 (yào) both mean “to want”. They are always placed before the main verb in the sentence to express feelings, obligation, or willingness to do something.

Rule
But, 想 (xiǎng) and 要 (yào) can be a different meanings.
想 means having the intention or desire to do, but not immediately. It can be “would like to” in English.要 means wants to do, it will be done right away. It can be “need”, “demand”, “order” depending on the context.

Structure
[Subject] + 想 or 要 + [Verb] + [Object]

Example

想 (xiǎng)		要 (yào)
我想去演唱会。 wǒ xiǎng qù yǎn chàng huì.	I’d like to go to the concert.	我要去看演唱会。 wǒ yào qù kàn yǎn chàng huì.	I want to go to the concert.
我想吃意大利面。 wǒ xiǎng chī yì dà lì miàn.	I’d like to have spaghetti.	我要吃意大利面。 wǒ yào chī yì dà lì miàn.	I want spaghetti.
我想喝咖啡。 wǒ xiǎng hē kā fēi.	I’d like to have a coffee.	我要喝咖啡。 wǒ yào hē kā fēi.	I want/ I need coffee.
我想看电影。 wǒ xiǎng kàn diàn yǐng.	I’d like to watch a movie.	我要看电影。 wǒ yào kàn diàn yǐng.	I want to watch a movie.
我想穿裙子。 wǒ xiǎng chuān qún zǐ.	I’d like to wear a skirt.	我要穿裙子。 wǒ yào chuān qún zǐ.	I want to wear a skirt.

Combining 想 and 要
Sometimes you can combine both 想 (xiǎng) and 要 (yào) together which becomes 想要 (xiǎng yào), which also mean to desire, to want.

我想要一杯果汁。
wǒ xiǎng yào yī bēi guǒ zhī.
I want a glass of juice. [probably said at a shop]

我想要预约在今天下午5点。
wǒ xiǎng yào yùyuē zài jīn tiān xià wǔ 5 diǎn.
I'd like to make an appointment for today at 5 pm.

我想要看一看尼亚加拉瀑布。
wǒ xiǎng yào kàn yī kàn ní yǎ jiā lā pù bù.
I really want to see Niagara Falls.

Expressing don’t want by adding 不 (bù)
Only 不 (bù) can be added to 要 (yào) and 想 (xiǎng). This form the words, 不要 (bù yào)、 不想 (bù xiǎng)、 不想要 (bù xiǎng yào).

Tips
Never use 没 (méi).

Structure
[Subject] + 不想/ 不要/ 不想要 + [Verb] + [Object]

Example
我不想走。
wǒ bù xiǎng zǒu.
I don’t want to leave.

我不要你走。
wǒ bù yào nǐ zǒu.
I don’t want you to leave.

我不想吃苹果。
wǒ bù xiǎng chī píng guǒ.
I don’t want to eat an apple.

我不要喝可乐。
wǒ bù yào hē kě lè.
I don't want to drink cola.

我不想要你回答。
wǒ bù xiǎng yào nǐ huí dá. I don’t want you to answer.