1. Explain it simply
想 (xiǎng) means 'want to' or 'would like to'. It expresses a wish or desire.
要 (yào) means 'want to', 'need to', or 'going to'. It is stronger than 想 and can express plans.
会 (huì) means 'can' in the sense of knowing how to do something (a learned skill).
能 (néng) means 'can' in the sense of being able to (having the ability or permission).
可以 (kěyǐ) means 'may' or 'can' - used to ask or give permission.
2. Show examples
我想做饭。
Wǒ xiǎng zuòfàn.
I want to cook.
想 = desire, wish
我要去上班。
Wǒ yào qù shàngbān.
I need to go to work.
要 = need to, going to
她会唱歌。
Tā huì chàng gē.
She can sing.
会 = knows how to (learned skill)
他不能来。
Tā bù néng lái.
He can't come.
能 = able to
我可以坐这儿吗？
Wǒ kěyǐ zuò zhèr ma?
May I sit here?
可以 = may, permission
3. Share a tip
To negate: 不想 (don't want), 不要 (don't / must not), 不会 (can't, don't know how), 不能 (cannot, not able). 不要 can also be a command meaning 'don't!'.