What do they mean? Source
To add a little to @abelenky's answer, you'll notice that each area has a identifier in it: SBR-522, SBP-505 etc. Those identifiers are made up of the ICAO country prefix, the airspace type, and a unique code. The airspace type can be Prohibited (P), Restricted (R) or Danger (D).
Since SB is the ICAO code for Brazil, SBR-522 is Brazil Restricted area #522; SBP-505 is Brazil Prohibited area#505 etc. I couldn't quickly see any nearby danger areas, but here's one in South Africa: FAD-193, near Port Elizabeth.
You can look up those codes in each country's Aeronautical Information Publication (AIP) or local equivalent to get more information about what each area is, what altitude it goes up to, any special rules etc.
See Page #10 of this document, which indicates that the markings show "Prohibited, Restricted and Warning Areas"
Where available, SkyVector uses FAA sectional charts to stitch together their
World VFR product. Where those are unavailable, my understanding is that SkyVector uses other available data to create their own charts. See this excerpt from a SkyVector product announcement (emphasis mine):
This chart is a "Sectional-style" VFR chart for use at low levels. For the United States, official FAA charts have been thoughtfully stitched together. For the rest of the world, topographical and aeronautical data have been sourced and assembled in a very high quality rendering.
Where SkyVector has used available FAA sectional charts, all chart depictions and symbology are provided by the FAA and follow the FAA charting guidelines laid out in the Aeronautical Chart User's Guide (Aero Guide) that @abelenky linked to in his answer. See this Aviation.SE answer for more information on that document and it's availability. Within SkyVector some of the same information can be found on individual sectional chart renderings.
Now, this is speculation on my part, but I understand that where SkyVector has used other topographical and aeronautical data to assemble World VFR charts outside the United States, they have chosen to use the same depictions and symbology for those charts. For this reason, the Aero Guide should be useable as a guide to understanding those renderings as well.