Break down the range of x values from -1 to 1, and y values from -1 to 1, each into 1024 parts (or whatever resolution you want to plot at). Evaluate the function for each (x,y) coordinate. If the resulting number is negative colour the pixel white, otherwise colour it black.

The expression is (probably) a 2d signed-distance function - https://en.wikipedia.org/wiki/Signed_distance_function