I've just downloaded the Arduino software. Can someone point me in the right direction as far as creating this program? All I need are forward and reverse and a consistent rpm.
I read your other thread. Designing a properly working system starts with a complete specification of what “working” means.
Seems to me that you didn’t even specify what you want the system to do if one of the motors slows down. Speed it up? Slow down the other one? Some combination of these choices?
After writing down your complete specifications, you may then need to learn a little about control theory. Then learn some programming. There are plenty of resources for that both online and built into the Arduino IDE.
Then, you take a stab at writing your program. If you run into problems or it doesn’t work properly you can bring it to a forum like this one for free advice. The better you describe the way you want it to work verses the way it’s actually behaving, the better that free advice will be.
Your other option is to pay someone to write your program.
What you want is a PID (Google "Arduino PID", then read up on how PIDs work in the real world) that is controlling velocity, rather than position. You can use the FreqMeasure library to calculate the velocity using one channel of the encoder as the input signal.
You don't really mean speed control, the other thread says you are keeping the motors in synch, so your error
variable is a position difference, not a speed difference. 2 wheeled robot?