You are deciding what product to sell, how are you picking the product? There are a few different type of ways to decide what product you pick.
WHERE TO START
There are three main types of ways of picking a product from manufactures: 1) dropshipping, 2) original equipment manufacturing (OEM), and 3) original design manufacturing (ODM). Dropshipping requires the least amount of resources to start. OEM and ODM will require more resources. Most e-commerce businesses start as a drop shipping business and scale their business to OEM then ODM. With more resources, you can also start with OEM and scale to ODM. See Product Choice Considerations.
PICKING DROPSHIPPING PRODUCTS
Dropshipping is pretty much bring the middleman between a manufacture and a customer. Most drop shippers set up their own website with the products they wish to sell. They will do the marketing and get customers to purchase their products through their site. The purchase information will be send directly to the manufactures and the manufactures will send it directly to the consumer. See Drop shipping Pros and Cons.
PICKING ORIGINAL EQUIPMENT MANUFACTURING (OEM) PRODUCTS
OEM products are products that are already manufactured and sold to a re-seller. The re-seller can either sell the product as is or have it re-branded with their own brand. This differs from drop shipping because you are actually purchasing the product from the manufacture and taking the physical property into your possession. See OEM Pro and Cons.
PICKING ORIGINAL DESIGN MANFUCTURING (ODM) PRODUCTS
ODM products are products that the seller designs and has the product manufactured according to the sellers own specification. ODM is similar to OEM, where you will be actually purchasing the products and taking physical possession of the product. The main difference is the seller will be able to design or engineer the product, as opposed to just purchasing a developed product by the manufacture. See ODM Pros and Cons.