The car has a particle filter or DPF, thisncaptures the soot that diesels generate, leaving a clear exhaust.
It needs cleaned out every 180 to 350 miles and the car knows when it needs done and looks for an opportunity, when the car is up to temperature and moving at a reasonable speed, it then manages the airflow and dumps fuel into the exhaust on the exhaust stroke, this sets up a high temperature burn in the DPF and the particles are burnt off.
It takes about 10 minutes, during which the MPG drops dramatically, the exhaust sounds a bit boomy and there is a burning smell. The turbo gauge will also drop like a stone when you lift off and if you stop, it will will sit at 10% boost, rather than zero.
When this comes on, try and keep the car over 3000rpm till it's over and alter your route so don't need to stop.
If you drive the car in town a lot, you might see it generate a warning that it needs cleared, I.e take it for a run as I described.
A forced regen is dome with diagnostic software and it's for cars that have been unable to regenerate on the road and are now too blocked to do so, ideally it needs physically checked over before doing so, also the car sits revving it's nuts off for 15 minutes, belching smoke with a glowing orange exhaust, it's not a sympathetic process and should only be done if absolutely necessary, and always with the bonnet open as it needs to vent a LOT of heat, it can melt the paint from workshop floors......so do it outside if at all.
You might read about a lot of issues on here with these systems, but believe me, Of DPF diesels of this age, the Fiat system is probably the most reliable and best.