(I'm a Joomla noob)
Had to look around a bit in the components section where nothing apeared, but then found the little "Insert Chart" button in the articles editor.
Every thing in the chart's window is pretty well explained if you have just a basic rememberance of how charts works from high school.
Only flaw I have come across, is that with the options mentioned in the insert page, there is no aparent way to change the Y axis from its default 0-100 range.
You can get it to show another range, but the actual apearance of data will still be based on 0-100. I haven't used Google charts before, so I'm not sure wether this is a flaw in google chart tools, or just a missing parameter that the dev of this extension forgot to put in, but it's most likely the extention that misses this.
So if you can live with to have to manipulate your actual data put into jv-chart to be on a 0-100% scale of the actual data and then just define the y-axis to the range you need to have shown this is a usable extension.
Its still easier to use this than calling google chart tools manually if people don't know how to do that
But if the dev of this extension is still active, some kind of fix would make this a very usefull extension.