Append the provider configuration to /etc/ppp/ppp.conf:
provider:
set device PPPoE:<interface>
set authname <PPPoE username>
set authkey <PPPoE password>
set dial
set login
add default HISADDR
enable lqr echo
enable dns
nat enable yes
set redial 2
Replace <interface> with your network interface towards the PPPoE server. Start the PPPoE client, as root: /etc/rc.d/ppp start
Enable PPPoE client at startup, append to /etc/rc.conf:
ifconfig_<interface>="up"
ppp_enable="YES"
ppp_profile="provider"
ppp_mode="ddial"
Start the PPPoE client with /etc/rc.d/ppp start as root. The PPPoE interface is usually tun0.