You can add creatures directly from the bestiary throw the menu at the top of each creature picture.
Public Bestiary
Log in or register to add creatures from your private bestiary.
Once you have added creatures, click or touch their HP progress bar to directly edit their remaining HP or click on +/- to add/remove 1 HP.
Click on the "Re-index" button to re-number the creatures if you have added/removed creatures several times and their numbering no longer helps you.