The left and right sides of the graph are the negative and positive sides of x respectively. When the values of x continues endlessly to the left, it tends towards negative infinity and if it continues endlessly to the right, it tends towards positive infinity.
The bottom and top sides of the graph are the negative and positive sides of f(x) or y respectively. When the values of f(x) continues downwards, it tends towards negative infinity and if it continues endlessly upwards, it tends towards positive infinity.
Considering the given graph,
As x tends towards negative infinity(the left), f(x) tends towards positive infinity(upwards)
As x tends towards positive infinity(the right), f(x) tends towards negative infinity(downwards)
