English generally expresses what will happen in the future, such as: I will go to Beijing tomorrow. But there will be some special forms in the future that express different meanings, and today we will study them together.
1. Be going to do: Used to express strong possibilities, certainty, willingness, etc.
例句1：I think it is going to rain.
I think it's probably going to rain. (Possibility of expression)
例句2：Watch out! That coffee is going to boiling over.
Be careful! The coffee was going to boil and spill out. (Expressing the certainty of the speaker)
例句3：When are you going to show me your new house?
When are you going to take me to see your new house? (Expression of will)
It's also worth noting that when expressing what is bound to happen, you can't use the sentence pattern of be going to.
（错） My son is going to be 18 next Monday.
My son will be 18 next Monday, which should be a fact, although in the future, this sentence pattern cannot be used.
2. Be about to do: When expressing actions that occur in the future, it is not used in conjunction with the adverb of time expressing the future.
（错）I am about to go swimming this afternoon.
Note that its negative form be not about to do is not an expression of the future, but of "not wanting to", which is equivalent to being unwilling to do.
例句4：I am not about to lend you books any more.
I don't want to lend you books anymore.
例句5：I am not about to give up.
I don't want to give up.