For low level windshear, visualize a column of cold air dropping from a storm, and spreading like an inverted mushroom as it hits the ground.
As you fly into it on approach, for example, you get lift from increasing headwind, followed by a downburst, and then a tailwind.
Reactive windshear systems, such as in GPWS computers, sense the change in performance once you have entered the shear, and give guidance for escape.
Predictive (really, Forward Looking) windshear systems imbedded in the plane's weather radar use doppler shift detection to identify microbursts up to two miles ahead.
Escape or avoid.
GB