A complement describes a verb's argument (subject or object) more closely:
1. Sir George is a knight. (Subject complement)
2. The Queen made Sir George a knight. (object complement)
Notice that you can put "a knight" in the object slot, in 2.:
3. The Queen made a knight of Sir George.
Notice that it is possible to read sentence 2. in such a way that "a knight" is, in fact, the object of the sentence. In that case, "Sir George" gets demoted from direct object of the sentence to indirect object of the sentence. The meaning of the sentence changes quite drastically. It now means:
4. The Queen made a knight for Sir George.
Because of what we know about the world, reading sentence 2. in a way that it means the same as sentence 4. is very unlikely, but grammar allows it.
So, in summary, the sentence # 2 could mean:
2. a The Queen (Subject) made Sir George (direct object) a knight (object complement).
2. b The Queen (Subject) made Sir George (indirect object) a knight (direct object).
So, I'm quite curious how to analyse a sentence like:
5. We changed train at Victoria station.
so that "train" is a complement. What does it complement? Since this sentence has no object, "trains" would have to be a "subject complement". But I don't see that.
It might be an "adverbial complement"?
I'm not sure myself.