my technique is to pick one of the hdri scenes in the scene wizard on startup. then one of the menus on the right has the place where ya select and load a new hdri, of which there are several in carrara content files. the technique for making hdri is non-trivial. If ya search this forum, there are old threads giving links to software and/or images. AFAIK one way to make hdri is to buy a reflecting globe, set it in the environment of interest, then take dozens of photos of it, spaced at 1 or 2 EV. these photos are such that the most underexposed has no white pixels, and the most overexposed has no black pixels. in addition, it's necessary to move around the dome when taking the photos, that the software might delete yer reflection.