Part of this comes from the confusing fact that Two-Weapon Fighting is both the name of a fighting style, and a special bonus action that every character has access to. The latter, the generic bonus action that anybody can do, tells you the following:

When you take the Attack action and attack with a light melee weapon that you're holding in one hand, you can use a bonus action to attack with a different light melee weapon that you're holding in the other hand. You don't add your ability modifier to the damage of the bonus attack, unless that modifier is negative.

If either weapon has the thrown property, you can throw the weapon, instead of making a melee attack with it.

The Two-Weapon Fighting fighting style states that "When you engage in two-weapon fighting, you can add your ability modifier to the damage of the second attack."

What you're seeing on your character sheet at level 1, likely under the Bonus Actions section of the Actions box, is the first ability quoted above. When you've reached level 2, however, and chosen Great Weapon Fighting, that is going to appear elsewhere on the sheet. As a class feature, you'll be able to find it in the Features & Traits box, nestled under Fighting Style.

If you'd like for the details of Great Weapon Fighting to appear in the Attacks box, so that you have easy reference to it and don't forget to use it, you can create a custom action on the sheet, and add the appropriate information, like so: