I'm quite new to Blender but planning to use it for 3D printing, so I'm looking for a solution which will actually modify the geometry. I have created a couple of aircraft. I need to detail them with some panel lines but I don't know how to easily make an indented straight line.
existing model - https://www.shapeways.com/model/1051048/d21-drone.html?li=my-models&materialId=6
The tools you are asking about are quite simple, you can make loop cuts with CtrlR. Roll your mousewheel to create multiple cuts and use left click to confirm/right click to cancel.
Since Blender can handle ngons, if your shape is a flat hard surface, feel free to cut it. Activate the Knife took with K, click an edge as a starting point and then click another edge as the end point, when satisfied. Press Enter to confirm.
You might also be interested in the Inset tool. This can be useful for giving your faces a bit of distance from the sharp edges so any further modifications don't look odd or modify parts of the mesh you don't want. Press I while selecting multiple edge loops or faces and use your mouse to adjust the inset level.
The Extrude tool is what you will use to create the indentations. Just select the face(s) and press E, you can use your mouse to adjust how far the extrusion goes in/out.
And all of those combined on a simple box model, produces this. Tri's aren't so bad when working with hard surface models but they make editing a pain.
Decent topology is a must when doing 3D printing. See, What exports does blender have for 3d printers?.
