Rolling two d20 when i attack

Hello,  I am new to Roll20, me and my friends will play for the first time today, I made my character sheet, but when I click my weapon (A quarterstaff), the roll20 rolls two d20 on the chat. Is that an intended mechanic? Thx for the help

It sounds like your sheet is set to auto roll advantage. You can change this behavior on the settings tab of your sheet. Many people leave it on all the time, taking the first (lefthand) value unless advantage or disadvantage is needed. In the latter case, they choose higher or lower according the the rule.

I'm not sure which system/character sheet you are using, but most that roll another die for critical confirm will roll both the attack and the confirm roll (in case it is needed) at the same time.  The confirm roll will be hidden in chat unless the main roll gives a chance for a crit.  Or, in the case of 5E, a second die might be advantage/disadvantage.