It takes time to get use to each other in the car. It is a relationship for sure.
!! L6/Cr>4 50 R5- into L3
"Double Cution left 6 over crest tightens to four 50 Right 5 minus into left 3"
You can look at notes this way. American rally notes go from up to down. The higher the number the less sharp the angle of the turn. Originally someplace someone had written notes to match gear speed. A 6 would be a 6th gear turn, a 4 would be a 4th gear pull and so on. They have since become standardized. It takes time to understand and picture in your head what the turn would look like. Some times people will use a more traditional worded set of notes and use terms such as "Easy, medium, sharp and so on". Most of the time ralliest get to pre-run the course. In america we call this "Recce". Which is short for reconnaissance. At that point driver and co-driver can write their own notes how ever they like.
Plus and Minus are simply "In between" Terms. A right four plus is slightly more open then a basic right four but not as open at a right five or right five minus. Obviously a right five minus is slightly sharper than a right five but not as sharp as a four.
There are other terms used to describe the course such as "crest, Cattle Guard, Junction" and so on. These are self explanitory.
When you hear numbers like 50, 30 or what ever, typically they are a distance in meters from one call to another. And into is obviously an "Into".