Welcome.
You login to your WordPress website by accessing either:
http://<your web address>/wp-admin
http://<your web address>/wp-login.php
From these pages you can edit your website pages, posts, menus, themes, images, plugins and so on.
You need to read some of the articles linked from this page:
https://codex.wordpress.org/Main_Page
Of course when you get stuck it is appropriate to start a new thread in the relevant support forum here.
You probably want to be able to access your old website while creating your new one, you will be able to copy+paste some or much of your content.