Your jump is limited by how far you can move; each foot jumped uses a foot of movement. You can take the Dash action if you want to extend how far you can move on your turn. For example, if you have a Strength score of 15, you can normally leap 15 feet when you make a long jump if you move at least 10 feet immediately beforehand. If the jump spell is cast on you, that potential jump distance is tripled. That’s a jump of 45 feet! If your speed is 30 feet, you can use only 30 feet of that jump distance on your turn, unless you take the Dash action, which allows you to leap the full 45 feet.