Do I have to open ports in my firewall?
If you have a firewall set up then you need to allow access to
UDP port 19132.
Do you want to use RCON? If so, then
TCP port 19132 also needs to be open.
On Windows, you might get a dialog like this when you first start the server. Click “Allow access” to allow PocketMine-MP through the firewall and allow players to connect.