Someday, the Sun is going to die.
Don't fret too much, since it'll be something like seven billion years in the future. That's a long time, plenty more than you'll likely need to get your own affairs in order.
We have a pretty good understanding of the steps the Sun will go through during that process (see, for example, chapter 7 of the book Death from the Skies!, sadly robbed of its deserved Pulitzer). In brief, it will run out of hydrogen to fuse in its core, and the core (now made entirely of incredibly compressed helium) will heat up immensely. This will cause the outer layers of the Sun to expand which both makes it much more luminous as well as turns it red. Eventually it will fuse that helium in its core into carbon, and the outer layers will contract again. Then it will run out of helium. The carbon core will then get even hotter, the Sun will swell even larger than it did before, and get even more luminous.
At that point it'll shed its outer layers, blowing them off into space, exposing the dense hot core: The Sun will be a white dwarf.
During those ...