Hello and welcome to LinuxQuestions,
You cannot migrate Active Directory to OpenLDAP one to one. You'll have to make a decision on what you want to migrate, for example users and take it from there. You might be interested in 389 Directory Server
or Calculate Directory Server
. Apart from that, don't expect LQ users to provide step by step guides, lots of them can be found on the internet. When you encounter problems following a howto, that's when you turn to LQ for answers.
Looking forward to your participation in the forums. Have fun with Linux.