After choosing the trigger event, you get navigated to a different page. This page will display the trigger event details. We have chosen the trigger as “On ERC20 Token Transfer”. This means when the trade is complete i.e. The address mentioned gets ZRX tokens, you will get a notification.
In the Ethereum Network dropdown, you get to choose between Mainnet and Kovan. You can select any contract address from the list. Now, the ‘when’ drop-down basically answers the question as to which event you would like to be notified.
For your reference the list is as such:
You can select 'On Token Receive' as the trigger event. So this means that you will be notified whenever there is a transaction and is completed, i.e. when ZRX tokens are added to the account. You then add the address for which you specifically want to be notified for. You can also add multiple addresses to this list.