For the open Arkansas primaries, voting day is Tuesday, May 22, 2018. To vote in either primary, you simply just have to request a Democrat or Republican ballot. Whichever ballot you request, your political party registration does not change. Paul will be on the ballot in the Democratic primary!
For the open Arkansas primaries, early voting will start on Monday, May 7, 2018 and last until Monday, May 21, 2018. In most counties of the Second District, you can early vote at your counties courthouse. See all the locations for early voting at the Arkansas Secretary of State's website, here.
The general election will be on Tuesday, November 6, 2018. There will not be ballots according to party as in the primary!