TrueType outlines use a different kind of math, quadratic Bézier splines instead of the cubic Bézier splines of PostScript outlines. Technically, this is actually simpler. However, it can be trickier to edit. The standard contour direction is reversed (clockwise for a filled contour, instead of counter-clockwise). TrueType nodes are on-curve points like PostScript nodes, but handles are connected to both the previous and the next point. Moreover, you may have any number of handles between two nodes.
TrueType offers much more sophisticated options for hinting than PostScript. FontLab directly supports this native TrueType hinting, but it does not require that the outlines be TrueType — you can do the TrueType hinting on PostScript outlines and let FontLab do the conversion at export time.
FontLab allows you to convert outlines from TrueType to PostScript (and vice versa), but if you wish to directly edit TrueType outlines without conversion or abstraction, FontLab can do that as well. Much more than FontLab Studio 5, FontLab today tries to apply the same modifiers and niceties to editing TrueType curves that work on PostScript curves. For example, many of the constraints and modifier keys have the same or equivalent effect, when moving a node or handle. However, some of the especially sophisticated features are not currently supported with TrueType curves. For example, AltShift does not allow you to slide a node along a curve.