How do you operate tri axle dump truck?

If you have experience operating a Class 8 truck, you should have the driving part down. If not, I would suggest you go to a truck driving school - you're not going to learn how by simply reading about it. As for the PTO controls, it depends on which PTO system you have. Normally, you push in the clutch, engage the main PTO control, let off the clutch, and use the secondary PTO control to raise and lower the dump body. Some systems differ, however.