I hope you are just looking at images that someone else took. Because without knowing all these terms you shouldn't operate an SEM! If you want to understand the basics of SEM, please google for some scripts/lectures or start with the wikipedia article.
To your questions:
WD means working distance and is the distance between your sample surface and the lower end of the pole piece where the electrons are coming from.
Det.Sec will be the detector of secondary electrons. This is a detector for low energy electrons that were extracted out of the sample by the hitting primary electron beam.
Det.in beam means the detector is inside the collumn. It is just some special SE detector that is not inside the chamber. Such detectors make it possible to work at very low WD.
The HV is the accelerating voltage for the electrons. So your electrons have 13keV energy.
I hope you are just looking at images that someone else took. Because without knowing all these terms you shouldn't operate an SEM! If you want to understand the basics of SEM, please google for some scripts/lectures or start with the wikipedia article.
To your questions:
WD means working distance and is the distance between your sample surface and the lower end of the pole piece where the electrons are coming from.
Det.Sec will be the detector of secondary electrons. This is a detector for low energy electrons that were extracted out of the sample by the hitting primary electron beam.
Det.in beam means the detector is inside the collumn. It is just some special SE detector that is not inside the chamber. Such detectors make it possible to work at very low WD.
The HV is the accelerating voltage for the electrons. So your electrons have 13keV energy.
I agree with Mr. Hoffmann above, you should probably stay away from the instrument until you get training. Now, just so you know the legend you see in your screen is particular to that instrument. Other SEM instruments might have different abbreviations/symbols and might be more or less user friendly, but they will surely refer to specs Mr. Hoffmann mentioned.
The AMMRF training module for SEM has a number of sections to work through before practicing on the "virtual SEM". I would recommend backing up to the beginning...
http://www.ammrf.org.au/myscope/sem/introduction/
The top level shows that there are modules for as well for TEM, XRD, AFM, confocal microscopy, and microanalysis.
http://www.ammrf.org.au/myscope/
The TEM module begins here...
http://www.ammrf.org.au/myscope/tem/introduction/
(This is going in parenthesis as I am going into pedantic mode, but I do have a few quibbles with the virtual SEM. The samples given are all, maybe with the exception of the sparker, non-conductive. Working with non-conductive samples in an SEM will require going into low vacuum (LV) or environmental mode (ESEM). Secondary electron imaging in these modes cannot be done with the common Everhart-Thornley detector. My understanding is that for most SEMs with LV and ESEM capability the only imaging mode at hand when not working at high vacuum will be the backscatter detector. Anyway, I feel this tool may give a misleading impression of how simple it is to work with non-conductive samples.)
I have been working with SEM images for the observation of microvascular networks of organic tissues, and very often find difficulties that the device manuals don't help.
I would like to thank Abbas Rahdar for his simple question that immediately led me to follow this question, in the attempt to learn some more from the comments of other friendly users of Scanning Electron Microscopy. I am thankful for the useful comments of Björn Hoffmann, Grant W. Pollard and Davis Barbier.