C++ help vectors + classes

General information for the business: coding
Description of requirements/functionality: I have begun experimenting with vectors, but can't make it work properly.
I have this class that I want to work with the vector. Before, when using arrays, it worked fine with this code:

Code:

int k=0;
Konto p[k];
p[0].konto("Per Pers", 100, 97986, 0.4);

The code is calling method konto in class Konto.
Trying to replace this with vector, I did the following:

Code:

vector vec;
int k=0;

vec[k].push_back(konto("Per Perss", 100, 97986, 0.4));

But now there's a warning at this last line of code, and it says "'class konto' has no member named 'push back' "


The job requested is to help me understand how to properly solve this, so that I can use vectors right. The aim is to be able to add more "kontos" within the program itself.
I am using CodeBlocks.
OS requirements: Windows
Extra notes: