Jazz-Blues in G-Bb
This is a simple jazz theme with a bluesy feeling, in keys of G and Bb (maj and min). You can watch the video lesson from YouTube and download some notation/TABS here. You know in jazz you hardly ever play the exact same thing twice, so, there will be very minor differences between the TAB and the video, but you will notice that yourself. It's not a mistake, it's just some freedom in playing a tune.
To improvise, the most basic thing you can do is use G and Bb pentatonic scales only. That will work, but is limited. You can do much more, as explained in part 2.