The program itSELF doesn't convert the image into 3D for you. You have to "build" the 3D part, OR....find one of those sites that offers free templates, and use a template that's pre-made. If you aren't very artistically inclined...I would suggest using templates.
There are quite a few sites that offer templates, as either a bonus to a product they offer, OR...just as a free gift on the site. Since I have numerous friends in this field, I hesitate to suggest just ONE of those sites. It wouldn't be fair to all of the others! Just do a search on Google for "free ebook cover templates", and I am sure you will have several to choose from.
IF you would prefer NOT to use a pre-designed template (and I would understand, as I am not personally fond of them mySELF), then you will have to build the 3D part of the image.
To do this in PI6 would take a tutorial that, well....I, unfortunately, don't really have the time to write at this moment! LOL
Basically, you use shapes (predominately rectangles) that you "stretch" to make the spine and the top back of the book, then they are merged to the 2D front. The shadow, and highlights are done using the air brush feature. That is what I use for highlights and shadows, anyway. I feel it gives the most realistic tones and shades of color, and is easily controlled.
I don't know if I have answered your question thoroughly enough for you to go DO this, but...if not...use a template. There are some very good templates out there, although they DON'T give the same realism as building the dimensions yourSELF...they are certainly sufficient for many uses.
Of course, if you make your cover and hate it....I'll still be around, and would be glad to help. That is why MANY, MANY people actually PAY to have their covers done. It saves YOU the time and grief of trying to get the effects you want yourself.
Peace and prosperity to you,
The industry standard of design for ePublishers