It's sometimes easier to work with Joomla initially by turning off many of the features that are on by default.

Login. Usually, there will be an Administrator menu if you are logged in as an admin. If not, that's ok. Go to your site/administrator/ ( This brings up the login page for the Admin Panel.

Dig around and check out the menus and options available.

I like to UnPublish all content except for a couple. This clears out some clutter.
Then, I UnPublish Modules I'm not using right away, like Polls, NewsFlash, Template Chooser, etc.

Menus - Unpublish menu items you don't need right away.

Now take a look at your site. It's stripped down, which should make it easier to get a feel of how you want it to look, and what features you want to add back.

Experiment. Remember to use UnPublish, versus Trash/Delete, while you are testing things out. When you trying out lighting, you don't remove the light bulb. No, you use the switch to turn it on and off. That's what the UnPublish feature is. On/Off switch. This is old (2006) and related to earlier versions of Joomla, and having the sample data pre-installed.