Vises are essential tools in fly fishing used to securely hold the hook while tying flies. They consist of a clamp or base, a rotating head, and adjustable jaws to fit various hook sizes. By stabilizing the hook, vises allow for precise and intricate tying of materials like feathers, threads, and synthetic fibers. This process creates realistic imitations of insects and other prey that attract fish. Vises vary in complexity and features, catering to both novice and experienced fly tiers, ensuring efficiency and creativity in fly fishing preparations.