*You can replace the first and second coordinate of the vector field below to experiment with different fields. The two exppressions in brackets, {x,-3,3},{y,-3,3}, stand for the range of x and y. Once you're done modifying your expression, hit Shift+Return (enter)*

*In 2D*

VectorPlot[{x,-y},{x,-3,3},{y,-3,3}]

*In 3D*

VectorPlot3D[{x,y,z},{x,-3,3},{y,-3,3},{z,-3,3},VectorColorFunction->"DeepSeaColors"]