A web designer focuses on the visual design and aesthetics of a website, using tools like Photoshop and Sketch. They are responsible for elements like color, layout, images, and user experience. A web developer works with website code, using languages like HTML, CSS, JavaScript, and server-side languages like PHP and Ruby. They take the visual designs and make the site functional by developing the code. Some people do both roles, but web designers typically focus on visual design problems while web developers solve problems through coding. The video provides advice for determining which role may be a better fit based on one's interests and strengths.