The axes first.

The y-axis is usually some unit of energy.  Sometimes, when it says relative energy or relative flux, there are no units posted since it is relative to the total flux of an object and you are only interested the shape of the spectrum.  If it is just energy, it has been summed over time and wavelength and is absolute, as opposed to apparent (telescopic).  Otherwise look for a per second (s-1); per wavelength (); or frequency; per area (cm-2, m-2). The last has factored in the area of the telescope and the distance from the object, i.e. it considers the number of photons flowing through an area at the earth (telescope).

The x-axis is either wavelength or frequency or electron volts (ev, kev). Frequency is herz (s-1).  Wavelength is angstroms () or nanometers (nm). One nm= 10 angstroms.

Try to remember your wavelength regions.  The units may give you a hint, as radio astronomers like frequency and x-ray astronomers like ev, while the rest of us prefer angstroms or nanometers.

Does the x-axis cover a large region, say a few multiples, like 100nm to 600nm, or is the entire range .01 of the values?  Most spectral lines are fairly narrow so they barely show up when a huge range is displayed, so you will see mainly the shape of the energy distribution. That may tell you temperature or a power law spectrum, but it is going to be hard to see any elements in emission or absorption. Maybe there will be enough resolution to see just a few strong lines.  Small measures of radial velocity will also be impossible to measure.

For a higher resolution you may lose the entire general shape of the spectral energy distribution.  You might get some slope or it could seem flat.  Then your interest should be the lines.  What elements are they? Is there any radial velocity?

Is the y-axis showing continuum, emission lines, absorption lines or some sort of combination?  Do you have any way to know how many light sources are contributing [think cataclysmic variable]?  If there is a continuum is it so faint that it is just noise and all you are seeing is an emission spectrum. DonŐt forget the astronomer has to use an exposure time that sees the targeted feature and that may mean underexposing or overexposing something else.

Spectra require longer exposures than images, but if they are done right that contain a LOT of information.