The basic settings should be:
/interface vlan
add interface=ether1 name=vlan848 vlan-id=848
/interface pppoe-client
add add-default-route=yes disabled=no interface=vlan848 max-mru=1492 max-mtu=1492 name=pppoe-out1 user=xxxx password=yyyy
/interface list member
add interface=pppoe-out1 list=WAN
and:
/ip firewall nat
add action=masquerade chain=srcnat out-interface-list=WAN
But there may be more settings needed and/or other settings that need to be changed from the default ones, so you should try adding the above settings, then follow this:
http://forum.mikrotik.com/t/forum-rules/173010/1
and post your configuration (remember to replace the personal data such as user/ password with dummies).