How do I achieve Two-Weapon Fighting and Dual Wielder?


I’m quite new to D&D and as we finished our first adventure with preset characters we want to play the next one with personal characters. We would start with lvl 1 in the new adventure.I want it to be a Dragonborn Renegade with two weapons. Im not quite sure if its should be a Barbarian or a Fighter.In my imagination this fits best with holding two weapons at the same time. And because I love longswords I would like him to have two at the same time. So i want him to have Two Weapon Fighter and Dual Wielder, but in the Character-Builder of DND-Beyond I don’t find an opportunity to combine the two skills.

And the final question: how would that work in a fight? so how does the rolling work for that if its possible to combine those 2.