help with analyzing PCA ( principle component analysis)

I'm reading a journal article on whole-genome sequencing and I dont know how to look at the PCA graph they have in the figures.

It says that PCA reveals continental and population specific patterns of genetic variation

PC1 - distinguishes Africans from non africans
PC2 - distinguishes Asians and Europeans

In the figure, there's just clusters of spots, some labelled to the hunter gathere population thats from the study, and other grey spots represented by non african.

What does the graph show though? I'm having a hard time understanding. Any help from someone with more experience would be grateful, I am only in 2nd year and we're given an assignment of reading this crazy journal article.