Our sun is about half way through its life, so will still be like it is for another 5 billion years or so.
It’s heat and light is generated by nuclear fusion, this is when 2 hydrogen atoms are fused together to make helium. This needs high temperatures and pressure. As the sun gets older and starts to run out of hydrogen this process will slow down.
This slowing will cause the sun to cool a bit making it look more red than yellow. It will also grow – a lot. It’s size will increase until it has expanded to thousands of times it current size – reaching out into space and engulfing the earth.
Because it gets bigger and redder it will be called a red giant.