Tonight at 7 PM CST, the Iowa Caucus will start. There are 41 pledged delegates and 8 unpledged delegates (super delegates: 5 DNC members, 3 Congressmen) in Iowa. The 8 unpledged delegates do not participate in the first round of voting at the convention so you don't have to worry about them.
Here is how the 41 pledged delegates are determined:
District 1: 7
District 2: 7
District 3: 8
District 4: 5
At large (statewide): 9
Party Leader/Elected officials: 5
So, what people need to understand is that this is a caucus and not a primary. There are no ballots and you don't vote for a single person and call it a day. Instead, this is a fairly arduous process where a bunch of people in each precinct meet at a public school or something like that and they listen to stump speeches for all the candidates. Then, they are told to stand in a corner to show support for a particular candidate. If a candidate doesn't have 15% of the vote at the precinct level, they are considered non-viable and their supporters can either support another candidate OR go home. For example, if Bernie gets 30%, Biden 25%, Warren 15%, Pete 20%, and Klobuchar 10%...Klobuchar supporters can reallocate at that particular precinct.
The viability threshold changes depending on the number of delegates at stake. Supporters of a VIABLE candidate are NOT ALLOWED to switch their vote. After that, the results are translated into "state delegate equivalents." Note, that the SDEs are predetermined in AMOUNT so if a particular precinct has insane levels of turnout, that doesn't affect anything. Lastly, only registered Democrats are allowed to caucus. No Republicans or Independents will be allowed to participate.
Reference:
https://www.thegreenpapers.com/P20/IA-DKnowing all this, who do you think will get the most delegates tonight? Note, that the results of tonight don't necessarily translate to ACTUAL delegates because the state convention doesn't occur until June (county convention occurs in March, District convention occurs in April)