Create an account. You can only have one account associated with an email address.
The next screen will ask you to choose a domain, or address for your site. As you type in a domain, you will see options for paid and free domains that are available. The option at the top of the list is free, and other options may be free for a year, but will require payment later. The free version of the domain will always be something.wordpress.com.
WordPress will append numbers to the domain you provide to create a unique domain, but if you keep trying different options, you might be able to create a domain that is unique without adding numbers.
You will see a choice of hosting plans, which offer different services. If you want a free site, click the link above the different plans. It’s labelled “Start with a free site.”