A star is a glowing ball of gas, heated by nuclear fusion in its center.
Stars are born in gigantic molecular clouds when gravity causes a region to collapse.
When the density and temperature in its center becomes high enough it starts creating energy, which halts the collapse and makes it shine.
When it has no more fuel left to keep it in balance, it dies; either with a bang
(if it's a massive star), or with a whimper
(if it's a low-mass star).