The top and bottom are histograms. They show the recent frametimes for CPU graphics (top) and physics (bottom) processing. Having a single tall bar is good, especially in the bottom one. No issues for you there. When you start getting a scattering of bars/dots it means the processing time is inconsistent, usually indicating excessive CPU usage and likely leading to timing issues. This can happen separately to overall CPU usage (the horizontal bars) which is why both are shown. The top histogram is generally less critical, as the spread of frametimes there can depend on sync settings etc, being the graphics processing. Still mostly consistent times (as shown by a taller bar or two) is good.
