The point of the graphs are as an example more than anything — in any real world solution it's not trivial to plot your documents (as representing documents with thousands of words in 1d, 2d or 3d is not trivial).
But if _you could_ represent your documents in 2d, you could plot them like I do here. And, the X-axis would represent 1 feature of your documents, and the Y-axis another.
Tl;dr don't focus on the axes — focus on the idea of being able to compare the relative distances between documents.
The point of the graphs are as an example more than anything — in any real world solution it's not trivial to plot your documents (as representing documents with thousands of words in 1d, 2d or 3d is not trivial).
But if _you could_ represent your documents in 2d, you could plot them like I do here. And, the X-axis would represent 1 feature of your documents, and the Y-axis another.
Tl;dr don't focus on the axes — focus on the idea of being able to compare the relative distances between documents.