well when you select import in the tools menu (which if you haven't already I'd recommend that you drag that drop down menu onto the left side of the UI, it'll make sculpting much quicker) it'll bring up the window for importation then you just select the model you want and hit import, have you been saving your models as .obj as thats its format of preference and i think it may even be all its able to import. well anyway i use .obj, if you still aren't able to import models it may be because its the trial however i remember being able to import models when i had it. hope that helped, i just got the full version last 2 weeks ago so I'm still learing a bit.