Question

how a thunderstorm formed

Answer 1

The Cumulus Stage
When warm, moist air moves upward in an updraft, puffy cumulus clouds may form in the atmosphere. The moisture in the air condenses into water droplets as it rises.  The cloud will continue to grow as long as warm air from below continues to rise.

There are several ways that an updraft of warm moist air can form.  Sometimes air is forced up the side of a mountain. Air is also forced upward at weather fronts, where warm and cool air masses collide. But often, updrafts form without a mountain or front to guide them – just because warm air rises. Air near the ground heats up during the day as energy from the Sun heats the ground, which then heats the air. The warmed air rises higher in the atmosphere because warm air has less mass than cool air, making it lighter.
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Answer 2

$\textbf{Thunderstorm}$:

The swift movement of the falling water along with rising are producing sound, lightning, heavy rain, and strong wind is called thunderstorm.

$\textbf{How Thunderstorm forms ? }$

Warm air rises and carry water droplets. At higher altitude the water droplets freezes and falls down towards the earth. During this The frozen droplets melt to form water droplets which falls in the form of heavy rain. This falling water along with the rising warm air and lightning give rise to a thunderstorm.

Two important characteristics will be : moisture, sea breeze or mountains as they provide help in formation of a thunderstorm.