How do you start and do this (complicated for me) parts of gears?
I was given this problem as my final output/project. I want to ask if they can give me a tutorial on how to make this figure. I think the values are not given so I think it's safe to assume to make your own value. And how to solve the speed of D?
(I'm not good at this)
It's something like that.
About your questions:
One speed is CW, one is CCW. One must be positive, other negative. You choose which, but usually we use "right-hand rule";
GR is the gear-ratio between first and last gears, as shown on the picture;
M is the module of the gear, in metric system we use module, so the primitive diameter is the number of teeth multiplied by the module;
To make gears I always use this http://www.thingiverse.com/thing:8077, there is a table, just edit the module and number of teeth;
The answer is negative because it was assumed -20 and +40, so it means the output has the same direction of -20 (CCW). Using right-hand, it would be +20 and -40, and the answer would be positive, again indicating same direction (CCW).