It is generated automatically on every railway switch that is properly built. It cannot be built separately, dismantled, or moved by any means.
A railway switch is formed by joining two Railways together at the end of a segment. It cannot exist immediately following or preceding a Train Station. Multiple tracks can be connected to the junction, the only limit being building space (therefore, it is possible to make a 15-or-more-way junction).
If the Railroad Switch Control doesn't appear, the track is not connected properly and the switch will not work.
Switching the switch is only doable by hand and it only affects trains with autopilot disabled. Automated trains ignore Railroad Switch Controls and always choose the desired track automatically, even if the switch is switched by another automated train.