D&D 5E Help with rolls during attacking

During one of my Roll20 games we were rolling attacking rolls with weapons but during the fight we had two rolls appear one was a number and the second was a number vs AC i understand how you do dmg and all thats fine i was just wondering what the first number represented vs the second one

Two d20 are rolled to account for advantage/disadvantage. If you have neither atm you just use the first one.

Both 5e character sheets do this deliberately. Every attack, save or ability check roll is deliberately made twice to allow for ease of use with the advantage/disadvantage mechanic that comes up frequently in 5e play. The intention is that if you are rolling with neither advantage or disadvantage then the second roll is ignored and only the first roll is used. If however you have advantage, then you choose the highest of the two rolls, and if you have disadvantage then use the lower of the two rolls. For more information regarding the Advantage/Disadvantage rule, please consult your 5e rulebook.

(Also, moving this to the Character Sheet forum)

Thank you very much!