I'm very new to modeling, and have no backround on it either! I am having some trouble with bones and meshes. Basically, I have the bones to be the parent of the mesh, however when I attempt to move them in Pose mode, they deform and scale in weird ways. I'm just trying to make some robot legs.
For some reason you've scaled your bone on its Y axis (Z global axis when the bone stands up) when you were in Pose mode. You need to select it in Pose mode and press altS to reset the scale. The parented mesh will come back to its normal proportion by the way...
If you want your bone to be longer than it is, you need to scale it in Edit mode, not Pose mode, which is made for animation. If you think that the Octahedral display mode is not convenient, you can switch to B-Bone mode for example, then you can change the bone thickness with ctrlaltS and drag.