How to copy string from one vector to another vector in C?

Question

I’m trying to create a program that will have a function called substring where the user will place the index position of an origin vector in which it will copy and the size of how many letters it will copy from this vector.

Example :

vetor_origem = "algoritmo"

substring(0,4) -- > "algo"

That is, I want the user to put the size of how much he wants to copy and from a position of the index, I already took a look at some other places, but I could not play right in the code.

But for this, I don’t know how I can go on. How can I do this ?