Well, to start with, the plot simply is decelleration over relative velocity. It does not guide you to your landing, it simply exists for noticing bad guidance inputs or allow manual control in a way that you are at least not dying instantly.
When properly initialized, the plot will move with the spacecrafts change in velocity, while the line plots the decelleration.
Now, its function is simple:
Those lines going down (read left to right) are called g-onset lines, and represent the maximum allowed decelleration at a velocity. The lines going up are non-exit g-offset lines and represent the minimum decelleration you should have to prevent skipping out of the atmosphere.
The top curved line, below which the other lines are drawn, is the maximum range G-limit. If you can't skip out, staying near this line ensures maximum range. If you go above this line, the capsule will stall and drop, resulting in LESS range.
Now - the big question is of course. Out of the many lines - which one should you follow? This is not to simple: When the plot goes down, stay above the g-onset line left to the plot. When the plot goes up, stay below the g-offset line left to the plot.
The dashed lines are range references. You can use them for comparing them to the AGC range to check if you are overshooting or undershooting.
The solid vertical line is the velocity, at which the spacecraft will be suborbital - from that point out you can now longer skip out.
