What shapes? all that depends on your preferences actually. Conical shapes look great as 'posts' for entrances, rounds look great if there are several in a row. Ball on top of square is yet another 'post' that looks great along entrances...

For topiary animals, typically you have to create as the plant grows and normally you'd need to create a frame that will help to shape the plant. So for established (meaning mature) plants, it's a bit more difficult to begin shaping because it may involve cutting back to bare branches. It will take years for new leaves to start filling out that space but at least they do grow back unlike some evergreens (thinking of junipers).

For your arborvitae (cedar), to shape it as a spiral is not difficult. Take a heavy cord or ribbon and coil it around the plant. Typically a minimum of 3 spirals or more (use odd nos.) and start pruning from inner to outer. Rounding the spirals as you go along. Step back to review yoru work every now and then. That's how it's done.