You can drag or paste an image into a text cell. You may also use the “Insert Image” button in the toolbar.
Images are copied to a resource folder inside the note, so they work even if the original images were deleted.
If you drag a file (e.g., PDF, zip, source files) into a text cell, you can choose to copy it into the note or save as a reference link. You may also use the “attach file" button in the toolbar.
URLs are automatically detected when you paste them into a text cell, for example, http://www.apple.com.
Another useful feature is Linked Notes. You can create a note link using the menu item “Copy Note Link” (⌃⌥⌘C) under the “Note” menu.
This is a nice way to cross reference your notes. A linked note can be in a different notebook, too.
Linked notes also work in Markdown cells. Use the menu item “Copy Note Link” (⌃⌥⌘C) under the “Note” menu to copy a note link, then paste it into a Markdown cell. For example,
It will be rendered as a note link in the preview or presentation mode.