These services can host your content on their servers free of charge, but in exchange for that zero cost, your online destination will have a less-than-elegant domain, such as jeffreylwilson.tumblr.com. That might be fine for a personal blog, but it will look too low-rent for a business that wants people to trust it enough to pay for whatever it's selling.
A website is a collection of many types of content. Your website can contain a collection of content including blog posts, product descriptions, images that highlight your product, explainer videos that tell your story, and contact information. These different types of content have one thing in common. Each piece of content has seconds to capture the attention of your audience.