You're doing well for a beginner. I found that the gearbox used to become a boxfull of grindy noises when I first started driving Crash box. Don't worry too much as the teeth are all being collected in the box. 😉
Ask if the transmission has synchronizers. I doubt it does since it is a truck. If it does not, you need to match the engine speed to the road speed for the gear you are shifting to once you move to neutral. I think people talk about double clutching. Clutch in when pull out of gear then clutch out while in neutral to spin the transmission at the speed you are going into then clutch out and shift into gear then clutch out. I have never driven a large truck. Only manual transmission cars.
If she said it's an 8-Speed there would be no blue splitter button so she also said it has the deep reduction in it so that would make it the 8LL that has the blue splitter button otherwise it would also be the 15-Speed