You need to have at least one feature layer loaded in ArcMap before you start this tool.
You should be careful about creating any buffers with data that is in a Geographic Coordinate System.
In these cases, one unit of measurement in the x axis (e.g. one second) is not equivalent to
the same unit of measurement in the y axis. This descrepency becomes larger the further away from the
equator your data is. In a Geographic Coordinate System a "perfect planar circle" would
actually look like an ellipse. If possible, use a coordinate system that minimizes distortion, like
UTM, State Plane, or for large geographic areas one of the Albers projections.