To log in to the Wordpress admin area, which is where you create pages and posts, you need to go to:
Wherever you see yourdomain.com in this documentation, replace it with your own domain name.
You will then see the login page.
Enter your username or email and enter your password.
If you want to have WordPress remember your details for a while - so you don't have to keep logging in every time - you can tick the Remember Me box (although don't do that on a public computer).