What is this graph showing?
This is a spectral energy distribution (SED). Since astronomical objects don't emit light a single frequency an SED tells you how much emission you're getting across a range of frequencies.


"log" indicates it's on a logarithmic scale
$\nu$ represents frequency in Hz (e.g. $log~\nu=12$ is $10^{12}$ Hz)
Jy is a unit of specific flux density $f_{\nu}$ is the specific flux 
MRK 1014 is the name of the object
Each of the points are observations there is a link on the page for "photometric data points" to see where everything comes from. All the positions have a point, which is measurement of the specific flux density at that given frequency. The vertical lines are the error bar for the flux measurement and the horizontal is the range of frequencies a measurement covers (e.g. a filter might have a central frequency but it filters light over a range of frequencies).
There are a few upper limits which are indicated by vertical lines with arrows pointing down.
LINE indicates that this is an estimate from a spectrum and it is the measurement of the flux of that line, not from a imaging filter.