# By default, each destination (name of new link) should not already exist
ln -s /home/user/project /var/www/html
# The link will be created inside /var/www/html having the name of the target i.e. project.
# If you want to have a symlink /var/www/html pointing to /home/user/project then you should not have the directory html present beforehand. So, you should only have /var/www and then running the following will create the desired symlink (don't do this unless you are sure)