I'm a complete beginner, trying to learn to use Blender 2.90.1 on an iMac (running Catalina 10.15.7). I've bought a hard copy manual but I'm stuck because, even though the software I downloaded is specifically for Apple, Blender seems to assume I have a PC mouse with three buttons (see bottom left of attached screenshot) and my mouse only has one button. Can someone help me with this?