Switcher the fixed track is located under the scenery tab. You won't find it under track - strange but true. Due to the way it's made. Track tab has spline track.
Spline Track works almost identically to model railway "flexi-track". You locate each end where you want it (Trainz will lay a piece of straight track between those points) and you then place a new spline point in between these two points, which is then moved to a location to create a curve, based on the spacial relationship of the three points (in effect, a "three point arc"). Alternatively, you can create all three points at once and Trainz will create the curve in one fell swoop. Unfortunately, there are no 'tools' per se that allow one to "set" the radius of the curve prior to laying track (just like real flexi-track - which requires a template of some sort to obtain a given radius), however, there are plenty of such templates available for download from the DLS - this where these template 'owners' jump in and give you their spiels...