Tools to start a blog, design one, promote it 

Blogger.com Widely used blogging platform by Google. Its free, fast, flexible and easy to use. Also allows to display your own ads and monetize your blog. Uses blogger/blogspot subdomain, but can point to your custom TopLeveDomain eg the domain you own.

WordPress.com Another free blogging platform hosted for free. Displaying ads is not easy to achieve, neither AdSense. You can sell products yet.

Self hosted domain is far better option than previous. You buy a domain, buy a hosting too (You may buy a hosting and get a domain for free) and you’ll have a complete site you own and you can controll. If you want to run a blog about a niche of your choose you’ll need to install WordPress script from WordPress.org or some other CMS (content management system), or a shopping cart if you want to run an online shop etc. Installing is done from a hosting control panel and is similar to any desktop software installing.