When you log into SongPad the first thing you'll see is your dashboard. This is where all your songs live. If you don't have any songs the only thing you'll see is the new song box on the top left of the screen.
To create a new song all you need to do is type a title into the new song box and click the plus icon. Don't worry if you're unsure about the title, its super easy to change it later. Once you've clicked the plus icon your new song is created and your taken to song editor... now the fun really starts!
If you're new to songwriting and need some tips on how to get started writing your lyrics, check out this article.