Future in the past.
First, there are several different ways to talk about the future in English.
All of these are usually described as "future tense":
I will go there.
I am going to go there.
I am about to go there.
When you are telling a story in the past, sometimes things will be in the future *for the story*, but you don't know if they are in the future for YOU, the speaker outside the story. So, you use "future in the past."
I will go there.--> He said that he *would go there*.
I am going to go there.--> He said that he was about to go there. I haven't checked with him yet, so I'm not sure whether he actually went there or not.
I am about to go there.--> He was about to go there, but I stopped him, so he didn't go there.