There are many ways to cover outlets, but this will make them inaccessible. Start with a standard outlet cover, which will cover all parts of the outlet except for the plugs themselves. \
You can insert plug covers into the plugs to cover the outlet. To hide an outlet entirely, move a piece of furniture in front of it or create a faux wall panel that can be moved to hide it behind. \
You can also use plants and other decorative objects to cover and hide an outlet on the wall. \