Linear will increase/decrease to the Intensity at a constant rate, while EaseInOut will smooth out the rate at the beginning and end. Like a car accelerating to top speed then gradually coming to a stop as it reaches its destination.
The Second Point Value is like a detour point before reaching the Intensity. The Second Point Location will determine when you reach that detour in the amount of time that you set. For example, if you set it 0 then the trigger will immediately start at the second point. If you set it to 0.5 then the trigger starts at whatever the current value is then reaches the second point after half of the total time has passed.