Don't worry about being a noob - we all were at one time or another.
Dropshippers - Companies that have products you can sell. The product stays in their warehouse until you sell it, pay for it, and tell them where to send it. Some of these companies are also wholesalers, but some are middlemen.
Wholesalers - Companies that get the products from the manufacturer and sell in bulk to you. You place your order, get your products, and store them yourself. After you sell a product you have to ship it out yourself.
Liquidators - Companies that get products from manufacturer's, stores, or other businesses. The difference between wholesalers and liquidators is that most products carried by liquidators have been on a store shelf at one point and these products are usually customer returns, over runs, discontinued or shelf pulls.
Manufacturers - the companies that actually make the products. Usually they only sell in large quantity.
Customer returns - stuff that people bring back for one reason or another.
Over runs - the manufacturer made way more than they had orders for.
Discontinued - last year's model.
Shelf Pulls - Brand new items that didn't sell and were taken off the shelf to make room for other things.
Hopefully that helps. Those are not by any means a comprehensive description of each type of supplier. I am sure that many others will be able to explain better.