I only learnt this today during school, but I'll try my best to share my limited knowledge.
I believe the markscheme is referring to the peak on the NMR graph, and the '2 CH3' is referring to the "environments" in which the hydrogens exist in the molecule, being that there are two of them, existing in the environment with CH3 surrounding it. You should watch some YouTube videos about it, it's a bit difficult to explain over text but lots of the practice questions I've been completing for NMR have a set structure to them. I suggest learning the 'core' knowledge and understanding for NMR off YouTube and then applying it to past paper Qs.