@Guilherme123 at what point are you stuck? do you have active service with public mobile or do you need to activate a new service?
If you do not have service you need a sim carrd first (walmart, londondrugs wow mobile kmovile all sell sim cards)
here is instructions for activating
Happy to help!
To make a payment with a voucher you have the following options:
1. Calling the IVR from your phone at *611 and going thru the steps to make the payment. (active Public Mobile account);
2. Log-in in your Self Serve account - go to Payments - Make a payment - One-time payment (pic attached) (activation or active account);
***Please note that you need to use the voucher's 12 digits PIN.