Instructions
Fight various monsters through random battles that you will encounter simply by exploring the world and moving around. From these battles, you may randomly obtain Ability Spheres after defeating certain monsters and you will also receive experience points with which you may travel the Sphere Grid.
Enter the Sphere Grid as Tidus and you will notice that for this character your starting location on the Sphere Grid is just 11 nodes away from the Ability node for Haste. Depending on how much progress you have already made with the Sphere Grid, you may be closer to the Ability than that. Count how many nodes away you are from Haste. This is how many sphere levels you will need to travel to this node.
Select the Haste Ability node once you have collected enough Sphere levels from battling to travel there. You may or may not activate the nodes before Haste, depending on whether or not you have the correct spheres for them or if you even desire them at all.
Press the X button when you are, on or next to, the Haste node and select "Use" from the menu that appears when you do so. Choose an Ability Sphere from your list of available spheres and the Haste node will be activated, meaning that your character, Tidus, has learned the ability Haste.