Twenty Democrats will take the stage over two nights this week at the first 2020 presidential debate. Here's some things you need to know to aid in your viewing.

Where and when is the debate?

With two dozen mainstream Democratic candidates running, the event is being split over two nights, Wednesday and Thursday June 26-27. Hosted by NBC News and convening in Miami, the debates begin both nights at 9 p.m. eastern and run for two hours. This is not unlike the early 2016 presidential debates that broke the Republican candidates into an early session and a late session on the same night.

Who is on stage each night?

In 2016, Republican candidates were sorted onto the two stages by popularity. The less popular candidates were relegated to the early debate stage; only Carly Fiorina was able to vault herself onto the main debate stage after beginning the campaign on the early stage.

For this debate, the 20 qualified Democrats were sorted by a random drawing.

Thus, Wednesday's debate will feature:

Sen. Cory Booker of New Jersey
Sen. Elizabeth Warren of Massachusetts
Former Rep. Beto O'Rourke of Texas
Sen. Amy Klobuchar of Minnesota
Former Rep. John Delaney of Maryland
Rep. Tulsi Gabbard of Hawaii
Former Housing Secretary Julián Castro
Rep. Tim Ryan of Ohio
New York City Mayor Bill de Blasio
Washington Gov. Jay Inslee

On Thursday, the lineup is:

Sen. Bernie Sanders of Vermont
Sen. Kamala Harris of California
Former Vice President Joe Biden
Mayor Pete Buttigieg of South Bend, Indiana
Sen. Michael Bennet of Colorado
Author Marianne Williamson
Rep. Eric Swalwell of California
Sen. Kirsten Gillibrand of New York
Entrepreneur Andrew Yang
Gov. John Hickenlooper of Colorado.

As a result of the random draw, Warren will not be going head to head against Biden and Sanders, who lead her in most polls.

So did polling affect debate postion?

Not for which night, but for which podium. Once sorted randomly into two lineups of ten candidates each. NBC then arranged the candidates on stage based on their polling averages. So on Wednesday, Elizabeth Warren and Beto O'Rourke will be center stage, while on Thursday it will be Joe Biden and Bernie Sanders at center stage.

Were any Democrats excluded?

Yes, about 165 Democratic candidates were excluded. Really.

People talk about there being 24 Democratic presidential candidates in the running, and that is kind of true — there are 24 candidates you might have heard of. Three of these candidates will not make the debate stage because they did not have enough individual donors or high enough polling averages: Gov. Steve Bullock of Montana, Rep. Seth Moulton of Massachusetts and Mayor Wayne Messam of Miramar, Fla. The fourth, former Rep. Joe Sestak of Pennsylvania, just announced his candidacy over the weekend.

But the Federal Election Commission has files for nearly 200 registered Democratic presidential candidates, though only about 35 of them have raised and spent any campaign money. So, yes, former Alaska Sen. Mike Gravel is running for president again, but the FEC at last count lists him as having raised no money. He will not be on the debate stage.

How much will we learn from the debates?

On the one hand, do the math: A two-hour debate with 10 candidates on stage means that on average, each candidate will get about 12 minutes of time — but that includes the questions. In reality, we are likely to learn precious little about the substance of the candidates' positions.

On the other hand, around 24 million people watched the first Republican presidential debate in 2016; for most of the Democratic contenders, that is a bigger audience than they have ever had. They will be straining mightily to make a favorable impression, whether with a new idea or a viral meme.