TUBE5 Celestion : I am a bit confused and i would like to receive help

Sticked to the end of the cable is a yellow written note, which states “this appliance must be earthed”. It makes me question half an hour of the practice time before i took a notice upon the note. Have i done damage to the amp by not following the instruction? What does it even mean that it should be earthed/grounded? Is the device incomplete?

The look, the feel, and the weight and the sound of it is beyond perfect, though i must say, i have been having issues with humming and constant ticking sound which seems to appear when i don’t lay hands on strings. It seems to wash away as soon as i lay hand on the string and play some notes.

Can someone pour remedy into my problem?