It automatically tunes the values of P, I, and D to your system.
http://milantrend.com/TDusermanual.pdf
If you are in "Automatic" mode the P/MV light will be off. Pressing SET will cycle between displaying the setpoint and the current power output (which will change based on how much power the controller thinks it needs)
If you are in "Manual" mode the P/MV light will be solid on. Pressing SET will cycle between displaying the setpoint (which doesn't actually do anything) and the current power output (which will stay at what you set it to)
If the "OUT 1" light is off, but the element is still getting hot, then you have a bad SSR or are wired up wrong.
If the "OUT 1" light is on solid, then the power output should display 100.
If the "OUT 1" light is blinking, then your power output should be something less than 100 depending on how fast it's blinking.
The questions you're asking seem to span more than one thing at a time, which might be making this more confusing.
There are two things going on:
1. You have a controller, which turns the element on and off. Compare the indicator lights on the controller with the indicator light on the SSR and the heat on the element to see if this is working the way you expect.
2. Your controller can use "smart" control to maintain a certain temperature. To do this, it needs to know values for P/I/D, otherwise the best it can do is plain old dumb control. You can either auto-tune the PID or manually pick values, but either way won't work if #1 isn't working.