A vector is a direction. It is in the same format as position, except it represents direction. Lets say your velocity is "10 0 0"
You are moving forward 10. "10 0 0" is a vector representing your forward movement. Now this vector has a magnitude (speed) of 10. To get rid of the magnitude (make it 1) you can do vectorNormalize(vector);. Type %player.getEyeVector() in the console. This returns a vector based on your eye sight. The values will be around 1 or less, and that is because that vector has a magnitude of 1. Here is the code used to return a position 5 units in front of where you are facing
%position = %player.getPosition();
%vector = %player.getForwardVector();
//Make the magnitude 5
%vector = vectorScale(%player.getForwardVector(),5);
//Add it to my position
%finalPosition = vectorAdd(%position,%vector);
I know I didn't do that well of explaining it, but thats how I started understanding it lol.