Your main duties would include:
understanding the clients needs, the target audience and the purpose of the website
preparing a design plan, with the site structure and linking of different pages
visualizing how the site will look at the front end
understanding how the site will work at the back end
designing the web page including type face, colors and backgrounds
using design software to make the page layouts
positioning buttons, links and pictures using design software
adding multimedia features like sound, animation and video
testing the design and site features
uploading the site to a server for online publication
updating the website and performing maintenance duties