What do you mean by "It's not a smooth running game." ?
The Minimum system requirement is
Processor: Intel Core i3-2125 (3.3 GHz)/AMD FX-4100 (3.6 GHz)
Memory: 4 GB RAM
Graphics: 1 GB, GeForce GTX 750/Radeon R7 360
and the Recommended system requirement is
Processor: Intel Core i7-3770 (3.4 GHz)/AMD FX-8370 (4.0 GHz)
Memory: 8 GB RAM
Graphics: 4 GB, GeForce GTX 960/Radeon R9 380
If your computer is on the low end of the requirements, check the Menu Options to see if you can turn down graphics enhancements and get it to run better.
If you are having trouble understanding what the potions and things do, be aware it's not a classic adventure style game. You may want to check a YouTube playthrough like this one to see how it's played.
https://www.youtube.com/playlist?list=PLj_Goi54wf0dNBY5-vdfAQlZSsWmTeQ44