Hi, welcome to Simviation

First of all, could you please edit your post to change the title into a more explicit sentence ? This would help when searching for informations

Then, for turning, you simply have to use your rudder axis, or the rudder axis AND the brakes, to trigger the differential brakes (brakes only on one side of the plane at a time). I think you will find the commands quite easilly in the plane control section, the name should be quite explicit. Sorry I cannot check myself right now, I'm at the office

Thanks for changing the title

Something I forgot to tell in my previous answer: some bi-engine propeeler planes do not have differential brakes. For those, a good trick is to use one engine at a time, plus the rudder.
So for example, if you want to turn left, you set your rudder full left, and simultaneously you increase the throttle of the right engine !

I don't remember the key combination to select one engine in the game, but if you fly from the virtual cockpit, then you can simply manipulate the throttle with the mouse