How does wind effect airplane take off and landings?

Aircraft always try to take off and land INTO the wind, as the effect of the wind flowing over the surface of the wing increases lift and therefore reduces the speed necessary to perform a take-off/landing.

For example, if an airliner has a computed take-off speed of 130knots, but there is a 10knot wind blowing directly at the aircraft during the take-off roll, the airliner only needs to achieve 120knots as the 10knot wind provides the extra to reach the required 130.

Of course it is rare that the wind will be blowing in the exact same direction as the alignment of the runway, which is why major airports have several runways, pointing in different directions. If there is just a single runway, aircraft may have to land or take-off in cross-wind directions. This can affect the control of the aircraft but safety dictates the maximum amount of cross-wind before it is deemed unsafe to land - usually in excess of 40knots.