A strut is part of the suspension system. It keeps the vehicle from bouncing around when driving over rough road conditions. When a strut goes bas, the vehicle will experience handling problems, uneven tire wear, and swaying and dipping. Some manufacturers recommend that a strut replacement be performed every 40,000 miles, while others suggest that the struts be replaced when they start to fail. Refer to your owner's manual to see when a strut replacement is necessary.
To replace the strut, the technician removes the tire and detaches the brake line from the strut. Then the cap covering the top if the strut is removed along with the cover to the strut assembly. Using a spring compressor, the technician tightens the spring and removes the nut at the top of the strut. Then the spring is decompressed allowing the strut to be freed from the spring. The old one is removed, the new one installed. Finally, the cover to the strut assembly is reinstalled, the brake lines reattached, and the tire is put back on.
You would be advise to follow the manufacturer's recommendations on how frequently to perform a strut replacement. If the strut fails due to a manufacturer defect or workmanship, then most manufacturer's will cover it under the bumper-to-bumper warranty section of the factory warranty. For extended coverage of a strut replacement, then an extended auto warranty is an option. Under certain levels of coverage, it will extended coverage to the strut after the manufacturer's factory warranty has expired.