Hello newuser8640,
Welcome to WordPress :-)
1) I recommend you take a look at WordPress' Custom Post Types:
http://codex.wordpress.org/Post_Types
http://wp.smashingmagazine.com/2012/11/08/complete-guide-custom-post-types/
Custom Post Types will allow you to create a post type called, "Products", for example, with fields including name, price, photo upload, etc. If you are coming from Drupal, this is similar to CCK.
You can create Custom Post Type programmatically, or using an easy-to-use drag and drop interface using third-party plugins. Two I recommend are:
http://pippinsplugins.com/easy-content-types/
http://www.advancedcustomfields.com
2) To control which users have access to create and modify the custom post types, I suggest you take a look at WordPress' Roles and Capabilities:
http://codex.wordpress.org/Roles_and_Capabilities
Once again, there are great plugins to make this easy if you want to avoid code. I recommend: http://wordpress.org/extend/plugins/members/
3) Finally, you may want to allow users to add new products from the front-end of your website, instead of forcing users to log into the WordPress' admin. There are a number of plugins which can help with this. I recommend:
Gravity Forms: http://yoast.com/gravity-forms-custom-post-types/
WP User Frontend Pro: http://wedevs.com/plugin/wp-user-frontend-pro/
Hopefully this gives you a good starting point for your website. :-)