How would you compare a red giant to our sun?
Our Sun will become a red giant in about 5 billion years
Our Sun is a small main sequence star. In its core hydrogen is being fused into helium.
In about 5 billion years, our Sun's core will be depleted of hydrogen. The core will start to collapse. At some point hydrogen in the layers outside of the core will become hot enough to start fusion reactions. At this point the outer layers of the Sun will expand out to about the size of Earth's orbit.
The Sun will then be a red giant.