How to express time delayed discrete signals
The problem with representing a discrete time just as a list like: $$x[n]=[6, 4, 0, 2]$$ is that you don't have a time reference. 

The first index $n=0$ or the sample in $\textbf{bold}$ or $\underline{\mathrm{underline}}$ is usually taken as the start of the sequence.

For example, $$x[n]=[\mathbf{6}, 4, 0, 2]$$ or $$x[n]=[\underline{6}, 4, 0, 2]$$ 

So $x[n-2]$ is a delay of two samples, and $x[0]$ now happens two samples later: $$x[n]=[\underline{0}, 0, 6, 4, 0, 2]$$