First of all if you are using installer which you seems to be you do not need to install anything separately. Alfresco installer comes with everything bundled into it's installation. Unless you have specific requirement where you want to use MySQL instead of bundled postgres database.
Now For workflow one everything is up and running you can check various existing out of box workflows available with alfresco if any of that meet your requirement you can use that directly no other efforts required.
In case you feel none of those workflow meetup your requirement then you need to create your advance workflow. http://wiki.alfresco.com/wiki/Workflow
This link contains all you need to know regarding alfresco workflows.