If you want to create a webpage on Joomla! the following process can be followed:
1. Choose a section (or create a new one)
Try and make sure this has a human readable and logical name. It will help you find things later on.
2. Choose a category (or create a new one)
Every category exists within a section. Again if these have human readable and logical names it will help you find stuff.
3. Write the article content
This is where the actual content is placed. Every article is assigned to a category and section ( even if it is “uncategorised” ). Articles are only published when you decide it’s appropriate. You can select which articles are eligible to appear on the front page.
4. Assign the article to a menu item
These exist completely independently of any page - a real difference from a conventional static website. This gives lots of flexibility. Whenever you choose to, you can assign articles to a menu item.
You can get more help about Joomla! and its terminology for non technical people here