What code is done first in a worker thread?

[Grear]

unsigned int ThreadProc(void*param)
{
    //processing
}

void buttonCLickEvent()
{
    //dosomething
    _beginthread(ThreadProc....);
    
   //do another thing
    if(bTrue)
    {
        //dosomethg
    }
    else
    {
        //do something else
    }
}

I would like to know whether the do another thing and its below codesnip will be called after or during the execution of ThreadProc. and Why is it ?
Thank you.