Yes, if you plot time along the x axis and distance along the y axis, the slope or gradient of the line or curve at any point (for a curve it's the tangent line at the point) is the speed. If the speed is constant, the graph will be a straight line; if there is acceleration or deceleration the graph will be a curve. Put it another way: if you see a graph of distance against time and it's a straight line, the speed is constant; if it's a curve there will be acceleration or deceleration. If it's a mixture of curves and straight lines, acceleration or deceleration is represented by the curved parts, while a constant speed has been reached for the straight parts. A horizontal line means there's no movement, i.e., the particle has stopped. If a graph starts at the origin and eventually drops back to rest on the x axis, the particle has gone on a journey and returned to its starting point.