I would like to create a website where users can post their products, but the payments, shipping and handling will be managed by the admin account, only one admin.
The admin will go to the users address, take the products, give them the money then delivers the product to whoever ordered it.
Which product should I use and how to get started ?
You may use Magento for this, but this will require customization to meet your requirement.
Do you mean a customization in php core or just customize some options in Magento ?