When you start a thread, it will execute until it is finished.
Often, at some point, you need to (possibly - the thread may already be done) wait for the thread to finish, because you want to use the result for example.
int n;
std::thread thread{ calculateSomething, std::ref(n) };
//Doing some other stuff
//We need 'n' now!
//Wait for the thread to finish - if it is not already done
thread.join();
//Now 'n' has the result of the calculation done in the seperate thread
std::cout << n << '\n';
You can also detach
the thread, letting it execute freely:
std::thread thread{ doSomething };
//Detaching the thread, we don't need it anymore (for whatever reason)
thread.detach();
//The thread will terminate when it is done, or when the main thread returns