On the photosphere of the Sun, the visible surface, there is granulation like the pattern, when the downflows cool down and gain a darker shade than the otherwise brighter upflows. These granulations are caused because of the flowing convection currents of plasma that occur in the convective zone. Inside the sun, all the reactions occur in a chain-like process and not at once, and because of the gas above the sun’s core and its extreme weight, the fusion occurring within doesn’t make the sun explode.