how to setup usg60 for L2tp vpn

hi everyone,
 i'm french, my english is not really good !! sorry !!

i just would like to know how to configure usg60 to allow windows vpn with l2tp auth.

it's not necessary to explane step by step but just all the things i have to do in the bigs lines.

what kind of ports open ? 
policy rules ? 
....  ??? 

i try a lot of thinks but cant found a full tutorial 

Thanks