My grandpa bought a Panasonic electric hair clipper and fancies cutting his own hair as he has little, but has questions about 'trimming height' and how to choose one. Can we ask them here?
From the information you give, the answer is probably 'no'. Asking how to use a tool, what its settings do and how to select them would be off-topic as there is no hack, just learning.
Cunning tricks and hacks around the settings could well be on-topic.
I can't think of a StackExchange site that would cover such grooming issues. This has been asked on the Main Meta before.