Couple things you need to consider.

First is the direction of the signal - auto signal can set routes towards the direction that the tip of the triangle is facing. You can change the direction of the signal in the build menu - first select the same type of signal as if you were placing a new one and then click on the existing signal you wish to change the direction of.

As for green, red and = symbol, green means that the route is set. Both the signal and the path ahead of it will be green. Red means that the track ahead is occupied by a train. When this happens, the signal will wait until the track is cleared before setting the next route. The = symbols are signals facing the opposite direction than the currently set route. Once the train passes the signal will opperate normally.

Perpetual circuits are the infinity signs that can be placed on an auto signal. They can either be grey or white, depending on their state - grey means inactive and white means active. The circuits are inactive after you place them. To activate them, click on the signal they're placed on, then press Shift (the circuit should appear white), and then set the route you want to be repeated. If the route is set (signal and track ahead is green) and the circuit is white, that means it's working. The circuit will then set that route as soon as the track ahead is clear.

As for a route using perpetual circuits, you can achieve full automation on a route like this, tho the reversing part might be difficult to achieve. I suggest referring to Silden's guide "Green - from beginner to intensive", as he explains it better than I can.

I hope that helped clarify things a little.
Edit: changed the last part because i was unaware of one trick that was much more efficient