要【yào】

要 covers wanting something and intending to do it. Before a noun it means "want"; before a verb it means "am going to".

要 is firmer than 想

想 wishes, 要 decides. 我要买 is a plan already made; 我想买 is still under consideration.

The negative is not 不要

不要 means "don't" – a prohibition, not a refusal. To say you do not intend to do something, use 不想 or 不打算.

This trips learners up constantly: 我不要去 sounds like a child stamping their feet, not like "I'm not going".

要 for what has to happen

With no sense of wanting, 要 can simply state a requirement.

要…了 for something imminent