We do host the reference broker under broker.portier.io (link to version endpoint). Our reference libraries set this as the default broker. It is okay to just use this for low volume websites, but if you have a lot of traffic or need to be sure that it is always online you should self-host the broker.
On the client site, you will have to implement the portier broker protocol. Instead of doing that manually you should use one of the libraries:
If you have to implement it manually you could use the demo implementation as a reference.
For reference, here are some sites that use Portier. Contact us if you want to be added to that list.