There are two ways that you can add Masks and Frames to your pictures in your photo book.
Once you have clicked on the picture that you wish to add a Mask or Frame to, if you have only clicked the image once, on the right hand side of your software will be a "Tools" menu, and inside here you will have options to Lighten and Darken your image, you can also Rotate the picture and add Masks and Frames.
When adding Masks and Frames via this method you are limited to 11 options of assorted Mask and Frames.
However, if you would like to choose from a bigger range of Masks and Frames, and also have a wider range of Creativity options (such as being able to change the colour of your photo, cropping, rotating, and adjusting the sharpness of your image) to have these options available simply Double Click the image you wish to Edit.
This will then display an Edit Image box:
Inside this Edit Image box you will have a range of options, and your last option will be Masks and Frames simply click into this Tab and you will then be presented with a drop down menu which will allow you to choose from either the Masks we have to offer or the Frames, you can then change the Width of the Border (only avaliable when using the frames) and also the colour.
Simply hit the "Apply" button once you have finished, and your chages will be saved onto picture.
(Always remember to save your project as you go along to avoid losing any work)