Here you go...from uncle Alex....
The genoa traveller normally dictates how much twist and Bag will the genoa or head sail have. Full forward will give you more bag, make the sail “more rounded”, and will normally give you more power, as the sail “camber” increases, causing more lift. Moving the traveller back will flatten the sail, making it more aerodynamic for stronger winds and or narrower pointing angles.
Think of it as a plane wing when its landing, they lower the flaps in the rear and the slats in the fron to make the wing have more lift, but speed is lower, if the plane was to fly faster that configuration would create too much drag.
To fly fast, the wing is really flat.
Traveler forward sail has more bag or curvature, traveller aft sail will be flatter.
How to set it, really comes with experience, as the wind picks up, or you point higher, a head sail with too much camber or bag (traveller forward), will stall sooner and start flapping, so as the wind picks up or you close the angle to the relative wind, you will need to flatten the sail (move traveller aft).
Start with the traveller in a central or mid position, in a position that is neutral. Then move the traveler forward, if you look at the sail, its bag moved towards the outside, this gives it more power, but less ability to point.
Then move it back and the sail becomes flatter, you will point higher, but have less power.
If the winds are weak, set them forward, slowly and see how the boat behaves, keep noting what happens when you move them, its intuitive.
If the winds are stronger, move the traveler back.
In light winds or when off the wind its normal to have the traveller forward, to increase twist on the sail, and as the wind picks up you will need to move the traveller backwards.
My traveller is controlled from the cockpit, we use genoa travel control when tacking (in some conditions), to help power the sails and accelerate the boat after it losses speed from tacking.
What we do is just before tacking we see where the traveler of the windward side is, move it forward if possible, then tack, the boat looses speed, but in this condition, with the traveler forward, the sail has more power, it helps accelerate, imagine 1st gear on a car, then as the boat accelerates, we start bringing the traveler back, and the genoa sheet also, and now that the inertia is gone, we shift 2nd gear....
So..start neutral, move forward for light winds and off the wind, and move backwards for strong winds and pointing higher.
If you have tell tales, start close hauled, and with traveler neutral (if you divide your luff in two, you found the middle of your genoa, the neutral position is one where the line between the middle of the luff, athe clew and the genoa car area straight line). Look at tell tales the ones where the wind is blowing from must be horizontal. Look at the bottom tell tale, if it is shaking and not horizontal, move the traveler aft, if the top one is shaking, move the traveler forward. Simple. Tell tales are best to get the car in right position.
Then there is halyard tension, backstay tension, shroud tension... bla bla bla .....comeback after yoiu found where to put the traveler we will explain the rest....
Here's a pic of my traveler with remote adjustment. Good very very good...
The next photo shows that under normal use, as you pull the sheets, the traveller wants to move back, we allow that to hapen by releasing the traveler control (that only pulls the traveler forward). Its the white rope that is loose
I really have to go, I am sure someone else here might help with better terminology.