Software testing is a crucial process to ensure product quality, identifying defects between expected and actual results, and involves several stages from requirement gathering to post-implementation. It encompasses various testing levels such as unit testing, integration testing, and user acceptance testing, using techniques like black box and white box testing. The software testing life cycle (STLC) consists of methodical activities including test planning, execution, and verification, emphasizing the importance of skillful testers and effective communication in the process.