The Maxwell-Boltzmann distribution shows the spread of molecular speeds (or kinetic energies) in a gas. Most molecules have speeds near the peak, but some are much faster or slower. The curve is not symmetrical — it has a longer tail to the right.
At higher temperatures, the peak shifts right and flattens out — more molecules have higher energies. The total area under the curve stays the same (same total number of molecules), but a greater fraction exceeds the activation energy Ea.
A catalyst provides an alternative pathway with lower Ea. It does NOT change the distribution — the curve stays exactly the same. Instead, Ea' moves left, so more molecules now have enough energy to react, increasing the rate of reaction.