i have to create few custom field like department, title, manager and map with active directory to automate the approval or reduce manual entries.
You can create Client Custom Fields and map whatever data you'd like to from AD into those custom fields.
Unfortunately, you can't map the manager name over to a Manager custom field and use that for an Approval Process.
You can, however, map Department over (without making a Custom Field, actually - you just have to make sure that "Departments" are enabled under Setup -> Companies and Locations).