First, you should make sure you log in to your site with the admin username/password that you selected when creating the site.  There is a link in the header of your site to log in.

A newly created site will have a simple activity-style home page, which has links to various tasks such as uploading new content, creating pages, making forum posts, etc.

On any page or directory, there are commands you can use simply by appending them to the address in your web browser.

mysite.example/pagename?browse  - browse the files in this directory
mysite.example/pagename?upload  - upload a file to this directory
mysite.example/pagename?edit  - edit page content
mysite.example/pagename?history  - show page content change history
mysite.example/pagename?log  - show detailed log, including all changes within contained pages or directories
mysite.example/pagename?type  - change the default page display type, which can be Page, Directory, or Forum

Remember, you can use these commands on any URL in your site, even the root one, for example mysite.example/?log to view a log of all site-wide changes.

You can create a new page simply by typing in the desired URL, and then clicking a special link on the 404 page, if you have adequate access level on the site.  You can also simply use mysite.example/?new and let the server figure out the best URL to use.

Once you are familiar with the basic operation, you can then customize your site.