In this chapter, Jotham becomes king and lives a relatively good life.
This is one of the shorter chapters in Chronicles, since it's only 9 verses total. It's also a relatively quiet chapter. Jotham seems like a good king, but unexceptional. The only notable accomplishment he has listed is defeating the Ammonites.
Honestly, we don't know a whole lot about Jotham. From verse 6 we know that he had a strong faith and he grew powerful. We are not told about him ever being defeated, and he has some building projects, and other than that we don't really know anything about Jotham at all. I checked the corresponding passage in 2 Kings 15 that also describes the reign of Jotham and it doesn't tell us anything more than what we read here. So, I guess I'll just say that Jotham is a decent enough king but he never did anything that was good or bad enough to deserve mention in these records.
I don't think there is anything else to say about this chapter, and in the next chapter his son Ahaz becomes king.