The easiest way is to create a songbook is when you are browsing a song. On each song page there is a button to the right of the title called "Add song to songbook"
Enter the title of your songbook in the input field and click "Create"
You might have to refresh the page to see your new songbook. Now, to add the song to the newl created songbook, click the little box to the left of the songbook title.
The little box should now show a little checkmark to indicate that the song is included in the songbook.
You have now created your first songbook! Congratulations!