How to lower/higher one surface without the neighboring surface making weird stuff I am currently building a ship model (18 century british navy ...) and I have a question ... 
I have looked at mirroring, so that my object is mirrored and I do not have to worry about forgetting an vertex or sth. similar. 


I want to higher the back part (with the marked edge).
However, when I do so 


this happens. 
I want the rotated surface to stay down (I otice only now, that I need mor room for the quarter deck, but that's not the problem here ... :-D ) 
This object does not need to be very precise, it is for a concept work (maybe I'll stretch it and improve some other stuff ... but basics first, right? :-D )
SIne I have worked with maya before, sadly not a student anymore, one could do this simply by exxpanding it, with blender, I have some trouble figuring out, how to do this ... 
any help would be highly appreciated, 
Karanda (yes, a David Eddings fan)
What you are looking for is called extruding in Blender (and most other 3d software).

Select the faces you want to extrude in edit mode and press E. In this case, the face will extrude along the z-axis. press  RMB to confirm the position.