Adding a second site to WP

I have a WordPress blog via WordPress.org. Now I wish to built a second website which has nothing to do with the first.
Obviously I’d prefer to be able to manage both sites from a single WordPress account, rather than logging out of one and into a second. Thing is, I’m not sure what the options really are. (I’m hoping that this is the correct place to be posting this question. If not please let me know).
Can anyone advise as to the easiest route for me to take?
Many thanks.