How to upload files for selling in the 'Buy,Sell,Trade' section?

I have posted a thread in the 'Buy,Sell,Trade'-Content section https://forums.digitalpoint.com/forums/content.76/ for selling 2 credit card articles. But I do not see an option to upload the articles that I want to sell. This is the first time I am selling something on DP, so am not aware of the procedure.
Sale thread - https://forums.digitalpoint.com/thr...ds-high-quality-original-seoptimized.2703672/
How to do it? Can someone please help?

 

Don you see the upload button like in the image below?



And why would you want to upload the articles, wont people be able to just steal it? Good luck!

 

Thanks for your reply devils_reject. So how do I sell them to someone who wants to buy? I mean, can you explain me the process please?

 

Any interested buyer will either post in your thread or PM you

After successful payment by PayPal, you deliver the item to buyer's email or through any file sharing site like Dropbox.com

 

I see. So, it goes like this. Thanks a lot for the info nihangshah.