What happens next?

How to buy prepaid cell phone cards online
Get an internet connection.
To buy online, you need to be connected to the internet, obviously. While you can do this on your laptop or desktop, you can also do it through your phone or any other internet-ready device.
Look for a good website that sells phone load for the network you may be using. It may be useful to add your country to the search term when you run a search online.