Looking at Standard Edition 2 limitations

From the documentation:

SE2 can be licensed on 2-socket servers where the current core counts run as high as 36-cores per server, and up to 16 threads per database instance.  For RAC you are limited to 2 1-socket servers and each instance will use up to 8 threads per database instance.

I've been told

"Threads are the number of instructions that a core can run simultaneously. So 1 core can have multiple threads and therefore run multiple instructions. The limitation here is that your DB can only use up to 16 threads (set of instructions run at a time). "

So is there some parameter that will limit the number of threads or is this done automatically?  Can you look at the number of threads that your database is using?