I will skip conversation pointers, as those choices are entirely up to you.
This chapter is really short.
After some conversations, you'll have to look for Clementine. She's outside; but once you go downstairs the game will force you into a conversation with Kenny and Ben first.
All other rooms in the manor can be searched for Clem but there's really no need, unless you want to talk some more with other survivors.
Once you get out into the yard, you'll get the achievement.