Note Pad Functions
The standard Apple "Note Pad" application from OS 9 kept a file with your notes in the System Folder. You could add new notes at any time by picking "New Note" from the file menu or by typing Command-N. You could page through the notes sequentially or find a string in a note with the "Find..." menu item.
Pads X works the same way. A default file is initially created with for your notes, although you may create new files and have more than one open at once (hence the application is named "Pads" in the plural). You can page through them by clicking the arrows above the text field, and the page number is shown on the bottom right. A new note is created with "New Page" or a Command-N, and a Find function is also available.
Just as there is no "Save" command in Note Pad, there is no "Save" command in Pads X. Whenever you make a change, the current page is saved to disk. (There is a "Save As..." command available if you want to save a copy of your Pads X document under another name).
A default document is opened when you open Pads X. Initially this file is created for you when you run Pads X for the first time. It is called "Notes.padsx" and resides in your Documents folder. You can change the name and location of this file in the Preferences dialog.