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.
Your website needs a place to live on the web, and the quickest way to reserve your web address is to find a web host. There are a variety of cheap web hosting providers, and each one has a specialty. Look for a web host that offers a price that fits your budget, has the web tools you need to create your envisioned website, and provides support when you need help or have problems.