Here’s a good graphic from the BIP32 wiki…
The variable k in the Addresses column is an increasing sequence of integers, each one representing a new public/private key pair (labeled as external and internal on the graphic). The specific format used by Counterwallet (and XCP Wallet for Chrome which is why they are compatible) to generate private keys is:
m/0’/0/k
k is 0, 1, 2, 3, … (since the sequence starts with 0 the 23rd address is actually k=22)