I have an Astra G selection 1.4, and near the oil dipstick I have a button that has a triangle and an exclamation mark. What is the use of it?
It is warning you to read the manual before you open it.
I assume that is is for the auto transmission that it is fitted to the car.
It looks like you lift the black handle 90 degrees to release the locking mechanism then withdraw the dipstick, but only under the conditions specified for that transmission.