how do you change the elevation of the track in the MSTS route editor?
Also, how do you add bridges in MSTS route editor?
To change elevation, select the track piece (press F2, then click on the piece), then press F4 and click and drag the piece of track up or down. Then press Y and the terrain will be brought up around the piece of track or taken out from under the track, depending on whether the track is going up/down. Make sure you save your track before you press Y if you haven't changed terrain elevation in a while, because MSTS sometimes crashes right here.
As for bridges, it's a little more complicated and I don't quite remember how to do it. Maybe somebody else will post here soon ...