The most dangerous are areas of strong upward winds near areas of strong downward winds (usually near thunderstorms).
A pilot flying near the ground might encounter a strong updraft. If the pilot then pushes the nose down to counterbalance, then the plane could suddenly enter a strong downdraft that, combined with the pilot still trying to descend from the updraft, can push the plane further down.
But technology to the rescue: Most aircraft are now equipped with wind-shear sensors, and many airports now have wind sensors along the tarmac to help alert pilots to wind shear potential. If a pilot knows it's coming, they can avoid problems.