On Canvas, content storage is separate from the content presentation. Most content is in the form of an uploaded file (Word, PDF, or Powerpoint files, typically) or a content page (a web page with text, pictures, and links, sometimes called a "wiki page" on Canvas). This means that all the files are stored in one place but displayed in another place (same with pages).
Uploading Files
To upload files, click on the "Files" link in the left-hand navigation bar. You'll see a list of all the files associated with your course, listed alphabetically. Use these links to upload and organize your files:
In some browsers, you may be able to drag & drop files into the files area.
This list of files is just a big list in alphabetical order, optionally organized in folders. This is the file storage. Typically, you would present the files to students in a meaningful order and organization by creating links to files on pages and within modules. See Organizing Content - Presentation.
For more details, see the official Canvas documentation on Uploading Files to Courses.
Pages
A Content Page is basically a web page within your course with text, images, and links. Canvas sometimes calls these wiki pages. (By default, students can't edit these pages, but you can make pages that students can edit.)
To view a list of Pages associated with your course, click the "Pages" link in the left-hand navigation bar. You'll either see a list of pages, or the "Home Page" if you've set one. Click the red "View All Pages" button to see all of the pages.
You can click on the red +Page button to create a page here, but typically you would create pages one at a time as you're constructing the course in the modules section.
Again, this list of pages is just a big list in alphabetical order. This is the storage of the pages. You present the pages to students by organizing them in order in the modules section, or by linking from the Home Page. See Organizing Content - Presentation.
For more details on editing a page, see Editing Pages.
Front Page
After you have created a page, you can designate that page as the "Front Page" of the course. To do this, go to "Pages" and if you don't see the list, click the red "View All Pages" button.
First: make sure the page is "published" (green checkmark symbol), then designate the page as a front page by clicking the gear symbol, then choose "Use as Front Page":
After you have designated a page as the front page, you can choose to display that front page as the home page of the course. Click "Home" in the left-hand navigation, then click "Choose Home Page" and choose the "Pages Front Page" option, then click Save.