A number of free blog sites are available where you can set up a free blog you can use to start an online business. The two biggest free blog sites are WordPress and Blogger.
You'll get input from a variety of sources about which free blog site is best to create your free blog. From a search engine optimization standpoint, WordPress is highly regarded. However, when it comes to simplicity, it doesn't get much easier than Google's Blogger in my opinion. Selecting and modifying your blog layout in Google's free Blogger is a matter of selecting and dragging and dropping elements around on the page. And, because a later step to start an online business business involves opening and setting up a Google AdSense account, a free blog from Google's Blogger can be an excellent choice for starting a free online business as it integrates very nicely with AdSense.
When you set up your free blog you'll need a title and will likely have an option on creating the URL that will be used to access your free blog. Use your findings from Step 2 - Search Engine Keywords to create a title and URL that will blend with your selected keywords.
While many will tell you that when you start an online business you'd be better off with a website for traffic than a free blog, website's come with hosting fees and considerably more maintenance than a free blog. The easiest way to start an online business is definitely with a free blog from a free blog site. As you grow and your knowledge increases, you might consider other alternatives.
Related topic: Getting Started with a Blog

