Chinese Grammar learning: 要不...
要不 (yào bù) can have a number of meanings depending on how it is.
要不 as to mark possible choices
要不 can be used to offer "either/or" choices to others, similar to 或者.
你 要不 看书 要不 听音乐 。
要不 你 做，要不 我 做，但是 一定 要 做 完。
Another word that can be used in a similar pattern is 要么, with the difference that 要么 can only be used to list the either/or choices available to oneself as well as the choices available to others.
要不 used for suggestions
要不 can be used as an indirect way of giving a suggestion, as the speaker is using 要不 to seek consent of the listener.
一个人去看电影没意思，要不 我们 一起 去 吧。
要不 我们 去 逛街 吧，比 在家 睡觉 有 意思。
要不 means otherwise
要不 can also be used to mean otherwise:
你 快点 打电话 给 他，要不 他会 很 担心。
我 要 打的, 要不 我会迟到。
我们 今 晚 需要 收拾 好 行李，要不 明天 来 不 及。
要不然 can be used interchangeably with 要不 when it is used as 否则.