I sorta figured out what 6 and 7 do, but not exactly how they do it...
They lock to the next visible target, in up or down direction.
what does button 3 do?
In the real radar, it changes the vertical sweep pattern of the antenna. Here's it's just for cosmetic purposes...
I need some help with the radar symbolgy... What do the numbers when I ID a target mean? 0.4 and 9? does that mean 4000ft and 90 kts?
Nope. Left number is Mach N. of the target, right number is absolute target altitude in thousands of feet. In this case, it was flying at Mach 0.4, at 9000 feets.
what about the numbers on the side of the radar mfd? 30.1?
That was reading -30.1. It's the altitude *differential* from the target, in thousands of feets. Since you were flying at 39000 feets and the target was at 9000, the differential was -30100, negative numbers indicates the target is below you.
Also, note the caret range symbol > on the right side of the screen, It's a visual representation of the target range, relative to the current scale. So, in this example, since you had the range set a 40, and the range symbol was slightly more than half screen, it was indicatin the target was at about 22 nm from you.