Using WordPress.com, create a new site.

+Add New WordPress

Big decision: you’ll need to decide on a site address. Since this is just a sandbox site for learning, don’t spend too much time trying to select something you’ll live with for years. You can do this again later when you have a clearer sense of what all these decisions really mean.

Next: choose a theme (you can change it later)

Finally: select a plan. Choose the free plan for now.

Voilà: you now have a site/blog!