Synonymous, hard to define.
Use 要 in case
you wanted to, need to , or had to. For example:
我要走了 I have to leave.
我要吃东西了 I have to eat something
我要买点东西 I need to buy something
他要我帮他拿东西 he asks me to bring him something
something/situation you can't refuse, or deny, such as
我要死了 I'm going to died
you need something, to get
他从篮子里要了个苹果 He grabbed an apple from the basket