Its quite simple, morons.
The graph is about exoplanets (it includes our solar system planets for reference). The x axis is mass, measured as a multiple of earth mass. For example, the number two on the x axis represents 2 times the earth's mass.
The y axis is radius, also as a multiple of earth's radius.
each triangle or circle represents an exoplanet with a known radius and mass. The little cross things are error bars. Our solar system planets don't have error bars because we know their radii and masses with high levels of precision.
The bars sticking out from the left are the number of planets discovered in each "bin", or with that narrow range of radius. They aren't all represented as data points presumably because we don't know their masses.
RV (circles) and TTV (triangles) are two different ways of determining an exoplanets mass. So each known exoplanet is shown as a circle or triangle depending on how its mass was determined.
The faint, gray dashed lines show the density of the planets.
I think the colored lines show the makeup of some aspect of the planet (core maybe?) although I don't understand how a planet can be 100% H2O.
The colored scale shows either the flux of the planet's magnetic field, again measured as a multiple of Earth's magnetic field, or the temperature measured using the Kelvin scale (of the core I presume) of the planet. The color of the dot or triangle tells you the flux, the color of the lines tell you temperature.
I'm not sure what topographic looking circles are, presumably some measure of something about the planets. The closer to the centers of those circles, the higher some value is. Each line represents a discrete change up or down from that value.
Finally, the curves along the x axis show approximately the frequency that planets with a certain radius fall into that mass range. For example, under the blue curve, you can see that most planets with a radius of 2-3 times Earth's radius have about 9 times the Earth's mass.