USB-c and Thunderbolt 3

Just built a PC that has a Thunderbolt 3 connector via USB-C connector. How do I connect something like the Ultrastudio Express (Thunderbolt via mini-displayport?) to it?

I see a few USB-c to mini DP adapters online, but they all are reviewed in reference to using a second monitor. Can I still use them for the Ultrastudio Express?

You will need a Thunderbolt 3 to Thunderbolt 2 adapter. Apple makes one as do some third parties (StarTech and Akitio), but the Apple one is actually the least expensive:
https://www.apple.com/shop/product/MMEL ... -2-adapter

In addition to the adapter, you will also need a Thunderbolt 2 cable to connect the UltraStudio Express to the adapter.

If you don't already have an UltraStudio Express, you might look at the UltraStudio HD Mini which has a similar feature set and built-in Thunderbolt 3 connectivity. Then you would just need a Thunderbolt 3 cable to connect to the PC.