Stitches are used to join fabrics and materials. There are various types of stitches classified into six classes based on their structure and method of formation. The most common types are lock stitch (Class 300), multi-thread chain stitch (Class 400), and covering chain stitch (Class 600). Each stitch type has distinct features and is suited for different applications based on factors like strength, elasticity, speed of formation, and suitability for various fabrics.