The sear is inside your trigger frame, the sear is used to catch the hammer/striker inside your gun and when you shoot the sear released the striker and causes the bolt to hit the ball.
The shim, is really to keep the spring straight so that when the striker is going back and forth, it will stay straight and not move around. On Spyders the shim is used to adjust velocity by adjusting it on the thumb adjuster. But torids velocity is adjusted by the amount of air/pressure going in your gun. you would need to adjust the regulator to match the velocity necessary.
The springs, the spring behind the stirker (under the bolt) is called the Main Spring, it is used to aid the striker move back and forth and the front spring (infront of valve) is called the valve spring used to move the valve back and forth.
When ever the striker strikes the valve the valve moves forward. When the valve is moved far enough forward the air is moved from the Regulator into the valve and the out at the end of the bolt hitting the paintball. Then the spring pushed the valve back to its original state and starts over again.
My wording might be a little off, but somebody might answer it a little better than I did.
Hope this helps!