This R squared value means that one variable does weakly predict the other. This low P value means that the odds of this happening by chance are low. So in other words racking up more miles in a year does weakly predict that I will gain more elevation over the year and the odds of my hiking more miles in a year causing my elevation to go up was not subject to mere chance. It's real, if I hike more miles in one year I will probably gain more elevation (duh). I have to look this stuff up every year because I forget what it all means.
Here is the same chart with one of the outliers eliminated the R squared value here is quite strong.The P value is unchanged because I did not run the statistical analysis without the outliers. Just ignore the P value on this chart as it is not correct.