How to manage Customer files

I have been manually entering orders when an item sells on another platform. I have been doing this to keep inventory accurate. I am wondering how can I get the buyers information into my customers file so that I can send marketing emails to people who have purchased from me.

Welcome to the Opencart forum. There are plenty of free import / export tools you could use from the extensions store on this site. For instance, you could use this tool: http://www.opencart.com/index.php?route ... load_id=44 .

I also provide database export which allows you store your Opencart customers database table on Excel files: http://www.opencart.com/index.php?route ... aightlight