New to the ownership of a diesel engine truck

I am new to the diesel engine world, this is my first diesel truck engine vehicle and I for one don't like not knowing what to do to maintain this bad boy.

What is DEF (diesel exhaust fluid) and what % does it have to be at? and when do I fill it uP? and is there a specific DEF?

Also whats the routine maintenance on these trucks? like at what mileage should i do certain upkeeps?

Ill check the manual later today, as i just bought the truck a couple days ago. I have read to do oil change and fuel filter change at 5000 mile intervals? is this correct?

and is it hard to change these out yourself? for those who are somewhat mechanically inclined?


THanks!