algebra precalculus - Summation of series of first $2n$ natural numbers and first $3n$ natural numbers

I am having an issue understanding the concept of the sum of the first $2n$ and $3n$ natural numbers.

So as I have gathered, the sum of the first $2n$ natural numbers is $n(2n+1)$, and the sum of the first $3n$ natural numbers is $(3n(3n+1))/2$.

But this is what is confusing me, $2n$ implies that it is $2+4+6 + \ldots$ or does it mean $2$ lots of natural numbers. It is really the way it worded is confusing me.